ZP proteins are responsible for sperm-adhesion fo the zona pellucida. ZP domains are also present in multidomain transmembrane proteins such as glycoprotein GP2, uromodulin and TGF-beta receptor type III (betaglycan).
The zona pellucida (ZP) domain is a protein polymerisation module of ~260 amino acid module, which is found at the C terminus of many secreted eukaryotic glycoproteins that play fundamental roles in development, hearing, immunity, and cancer [ (PUBMED:1313375) (PUBMED:12021773) (PUBMED:12878193) (PUBMED:15079052) ]. Proteins containing a ZP domain include:
Sperm receptor proteins ZP2 and ZP3. Along with protein ZP1, proteins ZP2 and ZP3 are responsible for sperm-adhesion to the zona pellucida. ZP3 first binds to specific sperm proteins, thus mediating sperm contacts with the oocyte. ZP2 acts as a second sperm receptor reinforcing the interactions. ZP1 cross-links the polymers formed by ZP2 and ZP3.
Zona pellucida sperm-binding protein B (ZP-B) (also known as ZP-X in rabbit and ZP-3 alpha in pig).
Glycoprotein GP2, the major component of pancreatic secretory granule membranes.
TGF-beta receptor type III (also known as betaglycan). This protein is a proteoglycan that binds to TGF-beta and could be involved in capturing and retaining TGF-beta for presentation to the signalling receptors.
Uromodulin (also known as Tamm-Horsfall urinary glycoprotein). The function of this protein, which is the most abundant in human urine, is not yet clear.
Chicken beta-tectorin, a major glycoprotein of avian tectorial membrane.
Most ZP domain proteins are synthesized as precursors with carboxy-terminal transmembrane domains or glycosyl phosphatidylinositol (GPI) anchors [ (PUBMED:12021773) ].
The ZP domain contains eight strictly conserved cysteines, which form disulphide bridges. The disulphide bonds within the ZP domains are divided into two groups, suggesting that the ZP domain consists of two subdomains. In addition to the conserved cysteines, only a few aromatic or hydrophobic amino acids are absolutely invariant, probably as a result of structural rather than functional constraints [ (PUBMED:1313375) (PUBMED:12878193) (PUBMED:15079052) ].
Family alignment:
There are 14185 ZP domains in 14113 proteins in SMART's nrdb database.
Click on the following links for more information.
Evolution (species in which this domain is found)
Taxonomic distribution of proteins containing ZP domain.
This tree includes only several representative species. The complete taxonomic breakdown of all proteins with ZP domain is also avaliable.
Click on the protein counts, or double click on taxonomic names to display all proteins containing ZP domain in the selected taxonomic class.
Literature (relevant references for this domain)
Primary literature is listed below; Automatically-derived, secondary literature is also avaliable.
Molecular cloning of chick beta-tectorin, an extracellular matrix molecule of the inner ear.
J Cell Biol. 1995; 129: 535-47
Display abstract
The tectorial membrane is an extracellular matrix lying over the apical surface of the auditory epithelium. Immunofluorescence studies have suggested that some proteins of the avian tectorial membrane, the tectorins, may be unique to the inner ear (Killick, R., C. Malenczak, and G. P. Richardson. 1992. Hearing Res. 64:21-38). The cDNA and deduced amino acid sequences for chick beta-tectorin are presented. The cDNA encodes a protein of 36,902.6 D with a putative signal sequence, four potential N-glycosylation sites, 13 cysteines, and a hydrophobic COOH terminus. Western blots of two-dimensional gels using antibodies to a synthetic peptide confirm the identity of the cDNA. Southern and Northern analysis suggests that beta-tectorin is a single-copy gene only expressed in the inner ear. The predicted COOH terminus is similar to that of glycosylphosphatidylinositol-linked proteins, and antisera raised to this region react with in vitro translation products of the cDNA clone but not with mature beta-tectorin. These data suggest beta-tectorin is synthesized as a glycosylphosphatidyl-inositol-linked precursor, targeted to the apical surface of the sensory epithelium by the lipid moiety, and then further processed. Sequence analysis indicates the predicted protein possesses a zona pellucida domain, a sequence that is common to a limited number of other matrix-forming proteins and may be involved in the formation of filaments. In the cochlear duct, beta-tectorin is expressed in the basilar papilla, in the clear cells and the cuboidal cells, as well as in the striolar region of the lagena macula. The expression of beta-tectorin is associated with hair cells that have an apical cell surface specialization known as the 275-kD hair cell antigen restricted to the basal region of the hair bundle, suggesting that matrices containing beta-tectorin are required to drive this hair cell type.
Transforming growth factor-beta (TGF-beta) signals by contacting two distantly related transmembrane serine/threonine kinases called receptors I and II. The role of these molecules in signalling has now been determined. TGF-beta binds directly to receptor II, which is a constitutively active kinase. Bound TGF-beta is then recognized by receptor I which is recruited into the complex and becomes phosphorylated by receptor II. Phosphorylation allows receptor I to propagate the signal to downstream substrates. This provides a mechanism by which a cytokine can generate the first step of a signalling cascade.
A large domain common to sperm receptors (Zp2 and Zp3) and TGF-beta type III receptor.
FEBS Lett. 1992; 300: 237-40
Display abstract
A new family of mosaic proteins is defined by sequence analysis. The family is characterized by a 260 residue domain common to proteins of apparently diverse function and tissue specificity: sperm receptors Zp2 and Zp3, betaglycan (also called TGF-beta type III receptor), uromodulin, as well as the major zymogen granule membrane protein (GP-2). The location of the common domain is similar with respect to putative transmembrane regions. The results lead to the hypothesis that this type of domain has a common tertiary structure and that there is a functional similarity in the recognition mechanism of the sperm receptor system and the TGF-beta receptor complex.
Structure and expression of the membrane proteoglycan betaglycan, a component of the TGF-beta receptor system.
Cell. 1991; 67: 785-95
Display abstract
We describe the primary structure of rat betaglycan, a polymorphic membrane-anchored proteoglycan with high affinity for transforming growth factor-beta (TGF-beta). As deduced from its cDNA sequence, the 853 amino acid core protein of betaglycan has an extracellular domain with clustered sites for potential attachment of glycosaminoglycan chains. These chains are dispensable for TGF-beta binding to the core protein. The transmembrane region and the short cytoplasmic tail of betaglycan are very similar to these regions in human endoglin, an endothelial cell membrane glycoprotein involved in intercellular recognition. The ectodomain of betaglycan can be released as a soluble proteoglycan; a potential cleavage site near the transmembrane region is identical to the highly regulated cleavage site of the membrane-anchored transforming growth factor-alpha precursor. The unique features of betaglycan suggest important roles in cell interaction with TGF-beta.
Expression cloning and characterization of the TGF-beta type III receptor.
Cell. 1991; 67: 797-805
Display abstract
The rat TGF-beta type III receptor cDNA has been cloned by overexpression in COS cells. The encoded receptor is an 853 amino acid protein with a large N-terminal extracellular domain containing at least one site for glycosaminoglycan addition, a single hydrophobic transmembrane domain, and a 41 amino acid cytoplasmic tail with no obvious signaling motif. Introduction of the cDNA into COS cells and L6 myoblasts induces expression of a heterogenously glycosylated 280-330 kd protein characteristic of the type III receptor that binds TGF-beta 1 specifically. In L6 myoblasts lacking the endogenous type III receptor, expression of the recombinant receptor leads to an increase in the amount of ligand bound and cross-linked to surface type II TGF-beta receptors. This indicates that the type III receptor may regulate the ligand-binding ability or surface expression of the type II receptor.
