Secondary literature sources for TY

The following references were automatically generated.

van De Graaf SA, Ris-Stalpers C, Pauws E, Mendive FM, Targovnik HM, de Vijlder JJ
Up to date with human thyroglobulin.
J Endocrinol. 2001; 170: 307-21
Display abstract
The coding region of the human thyroglobulin (TG) mRNA has been resequenced, and comparison with the TG sequence originally published in 1987 showed many variations. All of the variations were validated in 20-40 other alleles, and this resulted in the revision of 41 nucleotide positions. This review presents the revised wild-type human TG sequence, including all known exon/exon boundaries and additional data on the TG mRNA population, concerning alternative splicing and variability of the polyadenylation cleavage site. The amino acid sequence derived shows one additional, 12 changed, and 10 polymorphic residues. Protein characteristics, such as acceptor and donor tyrosine residues, N-glycosylation sites, cysteine-rich repeats, the proposed receptor domain, and antigenic epitopes, are included, and their relationship to the revised sequence is discussed. Furthermore, all reported TG mutations causing dyshormonogenesis in humans and animals are designated in the nucleotide and amino acid sequences. This up-to-date profile of the human TG molecule presents the features of importance for its complex role in thyroid hormonogenesis, and is the basis for future studies on the structure-function relationship.

Duthoit C et al.
Production of immunoreactive thyroglobulin C-terminal fragments during thyroid hormone synthesis.
Endocrinology. 2000; 141: 2518-25
Display abstract
Here, we studied the fragmentation of the prothyroid hormone, thyroglobulin (Tg), which occurs during thyroid hormone synthesis, a process which involves iodide, thyroperoxidase, and the H2O2-generating system, consisting of glucose and glucose oxidase. Various peptides were found to be immunoreactive to autoantibodies to Tg from patients and monoclonal antibodies directed against the immunodominant region of Tg. The smallest peptide (40 kDa) bore thyroid hormones and was identified at the C-terminal end of the Tg molecule, which shows homologies with acetylcholinesterase. Similar peptides were obtained by performing metal-mediated oxidation of Tg via a Fenton reaction. It was concluded that the oxidative stress induced during hormone synthesis generates free radicals, which, in turn, cleave Tg into immunoreactive peptides.

Lenarcic B, Krishnan G, Borukhovich R, Ruck B, Turk V, Moczydlowski E
Saxiphilin, a saxitoxin-binding protein with two thyroglobulin type 1 domains, is an inhibitor of papain-like cysteine proteinases.
J Biol Chem. 2000; 275: 15572-7
Display abstract
The type 1 domain of thyroglobulin is a protein module (Thyr-1) that occurs in a variety of secreted and membrane proteins. Several examples of Thyr-1 modules have been previously identified as inhibitors of the papain family of cysteine proteinases. Saxiphilin is a neurotoxin-binding protein from bullfrog and a homolog of transferrin with a pair of such Thyr-1 modules located in the N-lobe. Saxiphilin is now characterized as a potent inhibitor of three cysteine proteinases as follows: papain, human cathepsin B, and cathepsin L. The stoichiometry of enzyme inhibition reveals that both Thyr-1 domains of saxiphilin inhibit papain (apparent K(i) = 1. 72 nm), but only one of these domains inhibits cathepsin B (K(i) = 1. 67 nm) and cathepsin L (K(i) = 0.02 nm). Physical association of saxiphilin and papain blocked from turnover at the active-site cysteine residue can be detected by cross-linking with glutaraldehyde. The rate of association of saxiphilin and cathepsin B is strongly pH-dependent with an optimum at pH 5.2, reflecting control by at least two H(+)-titratable groups. These results further demonstrate that various Thyr-1 domains are selective inhibitors of cysteine proteinases with utility in the study of protein interactions and degradation.

Turk D, Guncar G, Turk V
The p41 fragment story.
IUBMB Life. 1999; 48: 7-12
Display abstract
The discovery of a fragment from the p41 form of invariant chain tightly bound to cathepsin L provided the first direct link between MHC class II molecules and the regulation of activity of lysosomal cysteine proteases. We recently determined the crystal structure of this p41 invariant chain fragment in complex with cathepsin L [EMBO J. 18, 793-803 (1999)]. This structure explains the specificity of the observed interactions and actually provides a tool, which can be utilized by means of molecular biology, to explore and understand the specificity of thyroglobulin type I domains and thus allow the design of specific inhibitors of papain-like cysteine proteases. The structure further supports the hypothesis that the thyroglobulin type I and II domains present in various proteins, sometimes in multiple repeats, are regulatory elements of the processing of these proteins by proteolytic cleavage.

Deshpande V, Venkatesh SG
Thyroglobulin, the prothyroid hormone: chemistry, synthesis and degradation.
Biochim Biophys Acta. 1999; 1430: 157-78

Dunn JT, Dunn AD
The importance of thyroglobulin structure for thyroid hormone biosynthesis.
Biochimie. 1999; 81: 505-9
Display abstract
Thyroglobulin (Tg) is the most important protein in the thyroid because it provides the matrix for thyroid hormone biosynthesis. Here we review experimental work, principally from our laboratory, on the relationship between Tg structure and hormonogenesis. Early work showed that Tg's most important hormonogenic site was located in a fragment of approximately 26 kDa obtained on chemical reduction. With the establishment of the cDNA sequence of Tg, this and other major sites could be localized within Tg's polypeptide chain. The four major hormonogenic sites, designated A, B, C, and D, are located respectively at tyrosyls 5, 2553, 2746, and 1290. In most species, site A accounts for about 40% of Tg's hormone, and site B for about 25%. Site C is associated with increased T3, at least in some species. Site D is prominent in guinea pigs and rabbits, and TSH favors hormonogenesis at it in these species. Sequential iodination of low iodine human Tg shows three consensus sequences associated with early iodination and with T4 formation. Recent work has identified Tyr130 in beef Tg as donor of an outer iodothyronine ring, most likely to Tyr5, the most important hormonogenic site. In addition to its biochemical importance, Tg has clinical interest in familial goiter and autoimmune thyroid disease. Further elucidation of Tg structure and its relation to thyroid hormone synthesis will contribute to thyroid physiology and to its clinical application.

Nlend MC, Cauvi D, Venot N, Chabaud O
Sulfated tyrosines of thyroglobulin are involved in thyroid hormone synthesis.
Biochem Biophys Res Commun. 1999; 262: 193-7
Display abstract
Thyroid hormone synthesis is under the control of thyrotropin (TSH), which also regulates the sulfation of tyrosines in thyroglobulin (Tg). We hypothesized that sulfated tyrosine (Tyr[S]) might be involved in the hormonogenic process, since the consensus sequence required for tyrosine sulfation to occur was observed at the hormonogenic sites. Porcine thyrocytes, cultured with TSH but without iodide in the presence of [(35)S]sulfate, secreted Tg which was subjected to in vitro hormonosynthesis with increasing concentrations of iodide. A 63% consumption of Tyr[S] (1 residue) was observed at 40 atoms of iodine incorporated into Tg, corresponding to a 40% hormonosynthesis efficiency. In addition, hyposulfated Tg secreted by cells incubated with sodium chlorate was subjected to in vitro hormonosynthesis. With 0.5 Tyr[S] residue (31% of the initial content), the efficiency of the hormonosynthesis was 29%. In comparison, when hormonosynthesis was performed by cells, with only 0.25 Tyr[S] residue (16% of the initial content), the hormonosynthesis efficiency fell to 18%. These results show that there exists a close correlation between the sulfated tyrosine content of Tg and the production of thyroid hormones.

Guncar G, Pungercic G, Klemencic I, Turk V, Turk D
Crystal structure of MHC class II-associated p41 Ii fragment bound to cathepsin L reveals the structural basis for differentiation between cathepsins L and S.
EMBO J. 1999; 18: 793-803
Display abstract
The lysosomal cysteine proteases cathepsins S and L play crucial roles in the degradation of the invariant chain during maturation of MHC class II molecules and antigen processing. The p41 form of the invariant chain includes a fragment which specifically inhibits cathepsin L but not S. The crystal structure of the p41 fragment, a homologue of the thyroglobulin type-1 domains, has been determined at 2.0 A resolution in complex with cathepsin L. The structure of the p41 fragment demonstrates a novel fold, consisting of two subdomains, each stabilized by disulfide bridges. The first subdomain is an alpha-helix-beta-strand arrangement, whereas the second subdomain has a predominantly beta-strand arrangement. The wedge shape and three-loop arrangement of the p41 fragment bound to the active site cleft of cathepsin L are reminiscent of the inhibitory edge of cystatins, thus demonstrating the first example of convergent evolution observed in cysteine protease inhibitors. However, the different fold of the p41 fragment results in additional contacts with the top of the R-domain of the enzymes, which defines the specificity-determining S2 and S1' substrate-binding sites. This enables inhibitors based on the thyroglobulin type-1 domain fold, in contrast to the rather non-selective cystatins, to exhibit specificity for their target enzymes.

Venkatesh SG, Deshpande V
A comparative review of the structure and biosynthesis of thyroglobulin.
Comp Biochem Physiol C Pharmacol Toxicol Endocrinol. 1999; 122: 13-20
Display abstract
Thyroglobulin, the major iodoglycoprotein of the thyroid (Mr 669 kDa) has a sedimentation coefficient of 19 S and an isoelectric point (pI) of 4.4-4.7. The protein has been isolated and purified from saline extracts of the gland of several animal species, by methods such as ammonium sulfate fractionation, DEAE-cellulose chromatography and Sepharose 4B/6B gel-filtration. DEAE-cellulose chromatography of thyroglobulin from many species, by linear gradient, yielded a complex elution pattern, while camel thyroglobulin showed only a major and minor peak. As an iodoprotein, the protein has 0.1-2.0% iodine. The amino acid and iodoamino acid composition of thyroglobulins, in general, is similar. However, a high thyroxine content (15 mol/mol protein) has been noted for buffalo species. Asparagine or aspartic acid has been reported as the major N-terminal amino acid for thyroglobulins of several animal species whereas glutamic acid is the sole N-terminal amino acid for buffalo thyroglobulin. As a glycoprotein, thyroglobulin contains 8-10% total carbohydrate with galactose, mannose, fucose, N-acetyl glucosamine and sialic acid residues. The carbohydrate in the protein is distributed as two distinct units, A and B. In addition, human thyroglobulin has carbohydrate unit C. The occurrence of sulfate and phosphate as Gal-3-SO4 and Man-6-PO4, respectively, has been reported in few species. The quaternary structure of native thyroglobulin is comprised of two equal sized subunits of 330 kDa. However, the protein appears to contain 4-8 non-identical units in few species. The synthesis of thyroid hormones occurs in the matrix of the protein and is regulated by pituitary thyrotropin. The role of tyrosine residues 5 and 130 in thyroxine synthesis has been well documented.

Dunn AD, Corsi CM, Myers HE, Dunn JT
Tyrosine 130 is an important outer ring donor for thyroxine formation in thyroglobulin.
J Biol Chem. 1998; 273: 25223-9
Display abstract
The thyroid couples two iodotyrosine molecules to produce thyroid hormone at the acceptor site in thyroglobulin, leaving dehydroalanine or pyruvate at the donor position. Previous work has located the acceptors but not the principal iodotyrosine donors. We incorporated [14C]tyrosine into beef thyroid slices, isolated and iodinated the [14C]thyroglobulin (Tg I), separated its N-terminal approximately 22-kDa hormone-rich peptide, and digested the latter with trypsin and endoproteinase Glu-C (EC 3.4.21.19). Nonlabeled thyroglobulin (Tg II) was isolated from the same glands and processed similarly, without iodination in vitro. Tg I was used to initially recognize pyruvate in peptide fractions, and Tg II was used to then identify its location in the thyroglobulin polypeptide chain. Sequencing of a tryptic peptide by mass spectrometry and Edman degradation showed a cleavage after Val129. An endoproteinase Glu-C-generated peptide had the predicted molecular mass of a fragment containing residues 130-146 with Tyr130 replaced by pyruvate; the identification of this peptide was supported by obtaining the expected shortened fragment after tryptic digestion. 14C-labeled pyruvate was identified in the same fraction as this peptide. We conclude that Tyr130 is an important donor of the outer iodothyronine ring. Its likely acceptor is Tyr5, the most important hormonogenic site of thyroglobulin, because Tyr5 and Tyr130 are proximate, because they are the most prominent early iodination sites in this part of thyroglobulin, and because the N-terminal region was previously found capable of forming T4 by itself.

Brix K, Wirtz R, Herzog V
Paracrine interaction between hepatocytes and macrophages after extrathyroidal proteolysis of thyroglobulin.
Hepatology. 1997; 26: 1232-40
Display abstract
Thyroglobulin (Tg), the precursor of the thyroid hormones triiodothyronine (T3) and thyroxine (T4), is known to derive from thyroid epithelial cells. Part of Tg reaches the circulation as an intact molecule by transcytosis across the epithelial wall of thyroid follicles. Circulating Tg is a potential ligand for the asialoglycoprotein receptor of hepatocytes. In this report we show, however, that clearance of circulating Tg occurred exclusively by endocytosis in liver macrophages, whereas hepatocytes did not participate in this process. The biological significance of this Tg uptake by the macrophages might consist in an increase of thyroid hormones in close proximity to the macrophages, thereby affecting the hepatocyte metabolism. To test this hypothesis, co-cultures of hepatocytes and macrophages were incubated with Tg, which resulted in the release of thyroid hormones and in a significant increase in the activity of lipogenesis and of hepatocellular key enzymes of the hexose monophosphate shunt. This effect of Tg could be mimicked by equivalent amounts of T3 or T4 exclusively in the co-cultures. When hepatocytes were incubated with thyroid hormones in the absence of macrophages, no or only little effect was observed, indicating that the interaction of macrophages and hepatocytes was a prerequisite for the stimulation of the hepatocellular metabolism. We conclude that the paracrine effect on HepG2 cells results from the degradation of Tg in J774 cells. Apparently, this process is not confined to the release of thyroid hormones, but it requires the interaction of both cell types, possibly mediated by an additional, as yet unknown stimulus.

Caturegli P, Vidalain PO, Vali M, Aguilera-Galaviz LA, Rose NR
Cloning and characterization of murine thyroglobulin cDNA.
Clin Immunol Immunopathol. 1997; 85: 221-6
Display abstract
Thyroglobulin is used to induce in mice experimental autoimmune thyroiditis (EAT), a model for Hashimoto thyroiditis. Because murine thyroglobulin is a more potent inducer of EAT than heterologous thyroglobulins, it has been hypothesized that it contains unique pathogenic epitopes. The validation of this hypothesis has been hampered by the lack of the murine thyroglobulin sequence. To identify murine-specific areas in thyroglobulin, we cloned, by reverse transcriptase PCR, and sequenced the complete murine thyroglobulin cDNA. This encodes a polypeptide of 2748 amino acids that is 73.5 and 71.8% identical to bovine and human thyroglobulin, respectively. Six regions are unique to each species. We also analyzed through EpiMer the sequences able to bind to the I-Ek major histocompatibility allele and, therefore, function as T cell epitopes. EpiMer analysis showed seven murine-specific T cell epitopes in thyroglobulin. The availability of the complete murine thyroglobulin sequence should promote the understanding of the pathogenesis and immunoregulation of EAT.

Kuppers RC, Hu Q, Rose NR
Mouse thyroglobulin: conservation of sequence homology in C-terminal immunogenic regions of thyroglobulin.
Autoimmunity. 1996; 23: 175-80
Display abstract
cDNA encoding 287 amino acids of the C-terminus of mouse thyroglobulin was cloned and sequenced. The amino acid homology between mouse and rat thyroglobulin was 96%, and was 78% between mouse and human. It was found that mouse thyroglobulin completely shared homology with two thyroiditogenic peptides described by other investigators. These findings are consistent with our hypothesis that in murine experimental thyroiditis, the primary thyroiditogenic epitopes are encoded by mouse-specific regions of thyroglobulin.

Mason ME et al.
Thyroids from siblings with Pendred's syndrome contain thyroglobulin messenger ribonucleic acid variants.
J Clin Endocrinol Metab. 1995; 80: 497-503
Display abstract
We studied thyroid tissue from two siblings with Pendred's syndrome (familial goiter and congenital deafness), both with the Mondini-type inner ear malformation, goiter, and hypothyroidism. Iodine trapping and peroxidase levels were grossly normal. Thyroglobulin (Tg), the only iodoprotein found, had a normal monomer size (330 kilodaltons), but low content of hormone and iodine. Tg's expected N-terminal peptides of 26 and 18 kilodaltons, usually formed in association with iodination and thyroid hormone synthesis, were absent, but appeared after iodination in vitro. Reverse transcription of ribonucleic acid from Pendred thyroid tissue and amplification by polymerase chain reaction of specific regions encoding the most important hormonogenic sites of Tg revealed a normal complementary DNA sequence corresponding to the first 100 amino acid residues in Tg's N-terminus. However, 3 of 35 clones of the 3'-region corresponding to the Tg C-terminus exhibited a deletion of nucleotides 7860-7994; this deletion was not present in any of the 150 clones from 7 other thyroids we examined. Four Pendred clones had a 2-nucleotide deletion at positions 7870-7871, a change that would result in a premature stop codon and was found in thyroids from several other subjects as well. We conclude that the messenger ribonucleic acid encoding the 3'-region of Tg can be abnormal in Pendred's syndrome. Some, but not all, of these changes also occur in other human thyroids. Further work is necessary to show if and how these alterations relate to defective hormone synthesis and goiter.

Xiao S, Pollock HG, Taurog A, Rawitch AB
Characterization of hormonogenic sites in an N-terminal, cyanogen bromide fragment of human thyroglobulin.
Arch Biochem Biophys. 1995; 320: 96-105
Display abstract
We have confirmed the observation of Marriq et al. (FEBS Lett. 207, 302-306, 1986) that substantial thyroxine formation occurs on enzymatic iodination of a 171-residue, N-terminal cyanogen bromide (CNBr) fragment of human goiter thyroglobulin. Marriq et al. concluded from their studies that Tyr130 is the donor for the preferential hormonogenic acceptor site Tyr5. However, in the present study we observed that thyroxine formation in the CNBr fragment occurred not at Tyr5, but rather at Tyr130. Moreover, we did not confirm the report of Marriq et al. that formation of thyroxine in the iodinated CNBr fragment involves cleavage of the Val129-Tyr130 bond. Our finding of thyroid hormone at Tyr130 was unexpected, as Tyr5 is known to be the major site of hormone formation in thyroglobulin isolated from the thyroids of humans and other mammals. In the CNBr fragment, however, Tyr5 appeared to act as a donor rather than an acceptor. Thus, while we have confirmed the finding that the N-terminal CNBr fragment of human goiter thyroglobulin is by itself capable of efficient thyroxine formation when enzymatically iodinated in vitro, we observed that the role of specific tyrosines in the hormone-forming process was different from that in intact thyroglobulin. We question, therefore, whether the CNBr fragment is a valid model for defining the role and location of hormonogenic sites in intact thyroglobulin.

Ieiri T
[Thyroglobulin (Tg) gene and familial Tg synthesis defect]
Nippon Rinsho. 1994; 52: 869-74
Display abstract
The thyroglobulin (Tg) gene is a 300-kilobase (kb) single copy gene, containing at least 42 exons, mapped in man to chromosome 8 (8q24) and codes for a glycoprotein with a molecular weight 660,000, which functions as a matrix for the thyroid hormone (T4, T3) and iodothyronine synthesis. Recent progress in genetic technology enables us to study a family case of hereditary goiter with hypothyroidism due to Tg synthesis defect. RT-PCR and subsequent sequencing of the Tg gene revealed a C to G conversion at -3 position of the acceptor splice site in intron 3. This splice site mutation resulted in exon. 4-deleted (major) and exon 3-5-deleted (minor) mRNAs in the goiter thyroid. This defect in this patient indicates the importance of the tyrosine No. 130, coded within the exon 4, in the thyroid hormone formation.

Brix K, Herzog V
Extrathyroidal release of thyroid hormones from thyroglobulin by J774 mouse macrophages.
J Clin Invest. 1994; 93: 1388-96
Display abstract
Thyroglobulin appears in the circulation of vertebrates at species-specific concentrations. We have observed that the clearance of thyroglobulin from the circulation occurs in the liver by macrophages. Here we show that the thyroid hormones T3 and T4 were released by incubation of mouse macrophages (J774) with thyroglobulin. Thyroid hormone release was a fast process, with an initial rate of approximately 20 pmol T4/mg per min and approximately 0.6 pmol T3/mg per min, indicating that macrophages preferentially release T4. The bulk of released thyroid hormones appeared after 5 min of incubation of macrophages with thyroglobulin, whereas degradation of the protein was detectable only after several hours. During internalization of thyroglobulin, endocytic vesicles and endosomes were reached at 5 min and lysosomes at 60 min. T4 release started extracellularly by secreted proteases and continued along the endocytic pathway of thyroglobulin, whereas T3 release occurred mainly intracellularly when thyroglobulin had reached the lysosomes. This shows that the release of both hormones occurred at distinct cellular sites. Our in vitro observations suggest that macrophages in situ represent an extrathyroidal source for thyroid hormones from circulating thyroglobulin.

Gentile F, Salvatore G
Preferential sites of proteolytic cleavage of bovine, human and rat thyroglobulin. The use of limited proteolysis to detect solvent-exposed regions of the primary structure.
Eur J Biochem. 1993; 218: 603-21
Display abstract
The sites and the sequence of the proteolytic cleavages of bovine, human and rat thyroglobulin, during the limited proteolysis with thermolysin and trypsin, were determined by sequencing the NH2 termini of the peptides produced and comparing them to the cDNA-derived sequences of bovine, human and rat thyroglobulin. Major cleavage sites of bovine thyroglobulin included residues 240, 502, 993, 1218, 1784 with thermolysin, and 240, 520, 1142, 1783, 2515 with trypsin. Cleavage sites of human thyroglobulin included residues 503, 982, 990, 1405, 1831 with thermolysin, and 522, 1627, 2513 with trypsin. Those of rat thyroglobulin included residues 501, 1776, 1784 with thermolysin, and 522, 1771, 1825, 2515 with trypsin (numbered as in bovine thyroglobulin). Thus, thyroglobulin from various species presents well localized and conserved regions particularly sensitive to proteolysis. The most sensitive region extended for 30 residues after residue 500. Another major cluster of cleavages was centered around residue 1800; this region was only partially sensitive in human thyroglobulin. A conserved tryptic site lay at the COOH terminus of the molecule. Most cleavage sites occurred within the inserted sequences that disrupt the Cys-rich, tandem repeats of thyroglobulin and either contain or are located near exon-intron junctions. Several cleavage sites lay in proximity of early iodinated or hormonogenic tyrosyl residues or of putative N-linked glycosylation sites. While a predominantly beta-type secondary structure and a rigid three-dimensional structure were predicted for the Cys-rich repeats, stretches of predicted alpha-helices, beta-strands and irregular structure were interspersed in the regions surrounding the cleavage sites. These data demonstrate the existence of conserved regions of thyroglobulin inherently sensitive to proteolysis, which most likely represent solvent-exposed regions of the primary structure, possibly forming loops at the surface of thyroglobulin.

Gentile F, Palumbo G
Trypsin-resistant regions of thyroglobulin: possible relationship with intermonomeric contact site(s).
Biochem Biophys Res Commun. 1993; 196: 1120-6
Display abstract
Upon incubation of bovine thyroglobulin with trypsin at high enzyme/substrate ratio, some fragments with apparent masses between 18 and 31 kDa resisted prolonged digestion. Their NH2-terminal sequences were determined. All fragments overlapped with some of the Cys-rich repeats that compose a large part of thyroglobulin and are predicted to have a rigid structure. Among the inserts that interrupt the cysteine-rich repeats, for which several data indicate a location at the surface of thyroglobulin, the insert of repeat 1.7 was unique because of its resistance to proteolysis. This insert, although exposed at the surface of the protein, may be hidden in a region of contact between thyroglobulin monomers.

Medeiros-Neto G, Targovnik HM, Vassart G
Defective thyroglobulin synthesis and secretion causing goiter and hypothyroidism.
Endocr Rev. 1993; 14: 165-83
Display abstract
The integrity of the Tg structure as a protein is essential for adequate synthesis of thyroid hormone. Also a large supply of iodine and of thyroid hormone is stored into the Tg molecule and available for secretion on demand. Mutations in Tg gene or hyposialylated Tg due to a defective sialyltransferase activity would cause a structurally defective protein and severely impair the functional ability of Tg. In this review we attempt to cover the abnormalities in the synthesis of Tg described in both animals and man. Hereditary congenital goiter with or without hypothyroidism is the phenotypic major clinical finding in these species. Affected animals include sheep, bovine cattle, bongo antelope, goats, and mice. As in man the inheritance mode is autosomal recessive. In most animal studies structurally abnormal Tg is present. The molecular basis for the defective Tg synthesis was attributable to nonsense mutation in exon 9 (Afrikander cattle) and in exon 8 (Dutch goats). In man the Tg defective synthesis has been reported in 89 subjects and frequently more than one sibling is affected in a given generation. Characteristically these patients exhibit hereditary congenital goiter with relatively low Tg levels that do not increase after stimulation with bovine TSH. High PBI concentrations with low serum T4 values indicate the serum presence of iodinated proteins (mainly iodoalbumin). Also iodinated peptides are frequently excreted into the urine. Tissue studies confirm that there is an absent Tg peak at gel filtration, and virtually no immunoassayable Tg is present in the tissue extracts. The molecular basis of these defects have been recently reported in a patient and includes low tissue Tg mRNA probably due to premature degradation of a defective Tg mRNA. The responsible mutation is a cytosine to thymine transition creating a stop codon at position 1510. The point mutation is removed by the preferential accumulation of a 171 nt deleted Tg mRNA. In another subject molecular studies revealed that exon 4 was missing from the major Tg transcript due to a cytosine to guanine transversion at position minus 3 in the acceptor splice site of intron 3. It is anticipated that other mutations responsible for these defects will be identifiable in the near future.

Herzog V
Regulation of the cellular transport and compactation of thyroglobulin.
Exp Clin Endocrinol. 1992; 100: 12-3
Display abstract
The cellular transport ot thyroglobulin in thyrocytes is a TSH-regulated process and characterized by a bidirectional export-, storage- and recapture pathway. The regulation of single steps in this pathway is unclear, but a possible basis for this transport appeared to be the presence of the lysosomal targetting, signal mannose-6-phosphate (M6P), on porcine thyroglobulin and the detection of the cation-dependent M6P-receptor on the apical cell surface and the Golgi-complex in thyrocytes. The question arose, why thyroglobulin is not directed on an intracellular pathway to lysosomes thereby following the route characteristic of lysosomal enzymes. Recent observations have shown that the affinity of thyroglobulin to the M6P-receptor is very low and the receptor is presumably not effective in thyrocytes to direct thyroglobulin to lysosomes. Instead, a low affinity binding site for thyroglobulin has been found to operate on the surface of thyrocytes. This receptor is specific for thyroglobulin and is saturable at 8-13 mg thyroglobulin per ml (5-9 microM). The highest affinity of thyroglobulin was that to itself which is the basis for the positive cooperation observed during binding of thyroglobulin to thyrocyte membranes. The receptor has a relative molecular mass of 46 kDa but is not identical with the cation-dependent M6P-receptor. Because of the high-thyroglobulin-concentration in the follicle lumen (100-400 mg/ml) it has always been argued that there is no need for the presence of a thyroglobulin receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Swillens S, Ludgate M, Mercken L, Dumont JE, Vassart G
Analysis of sequence and structure homologies between thyroglobulin and acetylcholinesterase: possible functional and clinical significance.
Biochem Biophys Res Commun. 1986; 137: 142-8
Display abstract
The homology between thyroglobulin and acetylcholinesterase (1) has been analyzed in detail. It contains 28.3% identical amino acids and extends over 544 residues, involving more than 90% of the acetylcholinesterase molecule and the C-terminal portion of thyroglobulin. The hydropathy profiles of the homologous regions have been determined and compared. Their striking resemblance suggests that both proteins adopt a similar three dimensional structure and militates for some common property. As thyroglobulin and acetylcholinesterase are known to interact with cell membranes, we suggest that the acetylcholinesterase-like domain of thyroglobulin is involved in the binding. These observations demonstrate that thyroglobulin has evolved from the condensation of a duplicated copy of the acetylcholinesterase gene with an archaic thyroglobulin gene encoding the major hormonogenic domain. The extensive homology in hydropathy profiles suggests that the two proteins may share antigenic determinants. If this were the case, it would provide a rationale for the demonstration of immunoreactive thyroglobulin in neurons (2) and the pathogenesis of Grave's ophthalmopathy.

Mercken L, Massaer M, Simons MJ, Swillens S, Vassart G
Identification of hormonogenic domains in the carboxyl terminal region of bovine thyroglobulin.
Biochem Biophys Res Commun. 1984; 125: 961-6
Display abstract
A segment of 986 nucleotides corresponding to the 3' end of the 8.5 kb bovine thyroglobulin (Tg) mRNA has been sequenced. An open reading frame of 302 codons was found, ending with TGA and preceding an 80 nucleotide long 3' untranslated sequence. The encoded protein sequence provided the first data on the carboxyl terminal portion of Tg. Lysine was identified as the last residue. Comparison of the amino acid sequence with that of peptides known to contain thyroid hormones in the mature protein, lead to the identification of three regions involved in thyroid hormone formation. Two closely linked thyroxine- forming sites were found 182 and 196 amino acids from the carboxyl terminus respectively. The antepenultimate amino acid of the protein corresponded to the recently described triiodothyronine-forming site. Together with the previous localization of the main thyroxine-containing peptide at the amino terminus, the present results provide a map of all hormonogenic sites identified to date in Tg.

Dunn JT, Kim PS, Dunn AD
Favored sites for thyroid hormone formation on the peptide chains of human thyroglobulin.
J Biol Chem. 1982; 257: 88-94

Rawitch AB, Hwan RY
Thyroglobulin structure-function: anilinonaphthalene sulfonate binding and the definition of nonpolar sites on native bovine thyroglobulin.
Biochem Biophys Res Commun. 1981; 100: 283-90

Chernoff SB, Rawitch AB
Thyroglobulin structure-function. Isolation and characterization of a thyroxine-containing polypeptide from bovine thyroglobulin.
J Biol Chem. 1981; 256: 9425-30

Pawelczak K, Rzeszotarska B
[Structure of thyroglobulin and its function in thyroid gland (author's transl)]
Postepy Biochem. 1980; 26: 559-83

Bagchi N, Brown TR, Shivers B, Mack RE
Role of the heterogeneity of thyroglobulin in the secretion of thyroid hormone in mice.
J Endocrinol. 1980; 86: 413-8
Display abstract
The rates of thyroglobulin hydrolysis and iodothyroine release from mouse thyroid glands were studied in vitro. Recently iodinated thyroglobulin ('new pool') had been labelled during life by injection of 131I 3 h before removal of the thyroid, 'old pool' thyroglobulin had been labelled by the administration of 125I in the drinking water for 1 week starting 3 weeks earlier. Chromatogrphic analysis of pronase digests of the thyroid glands showed that the iodothyronine content of the old and new pools were 19.5 and 7.4 per cent respectively. In the basal state the rate of thyroglobulin hydrolysis was lower from the old pool but the rate of hormone secretion was similar from both pools. Thyrotrophin (TSH) increased the rate of thyroglobulin hydrolysis and hormone release from both pools by up to four to six times the basal rate, the effect being maximal 2 h after administration of TSH and lasting for 6-8 h. The rate of thyroglobulin hydrolysis after TSH was similar in both pools but the rate of release of labelled iodothyronines was significantly higher from from the old pool. These studies have indicated that although hydrolysis of thyroglobulin paroceeds faster in the new pool than in the old ('last come, first served' hypothesis) neverrtheless there is no difference in the rate of hormone secretion from the two pools, and hydrolysis in both pools is affected by TSH.

Marriq C, Arnaud C, Rolland M, Lissitzky S
An approach to the structure of thyroglobulin. Hormone-forming sequences in porcine thyroglobulin.
Eur J Biochem. 1980; 111: 33-47
Display abstract
The mixture of CNBr peptides obtained by treatment of porcine thyroglobulin with cyanogen bromide was separated into three fractions by Sephadex G-200 gel filtration in 1 M propionic acid. When one of these fractions was reduced and S-alkylated, a hormone-containing CNBr peptide was purified by filtration on Biogel A-1.5 m and ion-exchange chromatography on DEAE-Sephadex. Similarly, two other hormone-containing CNBr peptides were separated from another reduced and S-alkylated fraction by Sephacryl S-200 gel filtration and DEAE-Sephadex chromatography. The three purified CNBr peptides have the same Mr (15000), differ in amino acid composition and contain 60-70% of the hormones present in the initial thyroglobulin. Fragmentation of these peptides into smaller hormone peptides was carried out by trypsin digestion followed by gel filtration. This resulted in the purification of eight discrete hormone-containing tryptic peptides whose homogeneity was established by the study of their N-terminal and C-terminal sequences. At least four sites for the synthesis of thyroxine and two sites for the synthesis of triiodothyronine have been identified in the three CNBr peptides. A possible additional site was recovered in the form of the peptides seryl-triiodothyronine and probably seryl-thyroxine. To gain information on the number of hormone-forming sites in thyroglobulin iodinated in vivo and on the distribution of these sites in the different hormone-containing peptides isolated, estimation of thyroxine and triiodothyronine content of batches of thyroglobulin of iodine content comprised between 0.73% and 1.6% was carried out, together with the estimation of the hormone content of all the CNBr peptides separated from two preparations of thyroglobulin of different iodine contents (0.73% and 1.23%). It was shown that the number of thyroxine and triiodothyronine residues increased linearly with increasing thyroglobulin iodine content in the range 0.73-1.6% and reached six residues of thyroxine and two residues of triiodothyronine/mol protein for a thyroglobulin iodine content of 1.6% with no indication of saturation. This result is at variance with previous findings on porcine thyroglobulin iodinated in vivo which suggested that the thyroxine content reached a plateau of three to four residues/molecule for an iodine content comprised between 0.7% and 1.1%.

Burrow GN, Eggo MC
Synthesis of thyroglobulin.
N Engl J Med. 1980; 302: 179-80