Taxonomic distribution of proteins containing SO domains

The SO domain within your query sequence starts at position 27 and ends at position 67, and its E-value is 3.3e-3.

Homology of placental protein 11 and pea seed albumin 2 with vitronectin.

Jenne D
Biochem Biophys Res Commun. 1991; 176: 1000-6

Vitronectin (complement S-protein), a plasma and tissue glycoprotein of 75 kDa, shares the amino-terminal somatomedin B domain with the membrane glycoprotein PC1 of plasma cells and several hemopexin-type repeats with hemopexin and the non-catalytic carboxy-terminal domain of collagenases. It serves as a ligand for certain integrin receptors, binds to distinct members of the serpin family and inhibits the pore-forming cytolytic reaction of the terminal complement pathway. Computer-assisted data base searches revealed the presence of a single somatomedin B domain in the recently cloned placental protein 11, and four hemopexin-type repeats in the cytosolic plant protein PA2, the major albumin of pea seeds, whose function is unknown. Our finding shows that hemopexin-type repeats are present in extracellular as well as in cytosolic proteins and most likely originated before the divergence of the animal and plant kindoms.

Evidence that type 1 plasminogen activator inhibitor binds to the somatomedin B domain of vitronectin.

Seiffert D, Loskutoff DJ
J Biol Chem. 1991; 266: 2824-30

The interaction between type 1 plasminogen activator inhibitor (PAI-1) and fragments of vitronectin (Vn) was investigated. The PAI-1-binding domain was not destroyed when Vn was cleaved by treatment with either acid or CNBr. Acid-cleaved Vn was fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and analyzed by PAI-1 ligand binding. The smallest fragment (Mr 40,000) that retained PAI-1 binding function was sequenced and shown to contain the NH2 terminus of the molecule. Further cleavage of this fragment by treatment with CNBr generated a Mr 35,000 fragment (Pro52-Asp239) that did not interact with PAI-1, and a Mr 6,000 NH2-terminal fragment (Asp1-Met51) that spanned the somatomedin B domain and contained the RGD (cell binding) sequence. The purified Mr 6,000 fragment competed with immobilized Vn for PAI-1 binding, and formed complexes with activated PAI-1. These complexes could be immunoprecipitated by antibodies to PAI-1. Synthetic peptides containing the RGD sequence had no effect on the binding of this fragment to PAI-1. These results suggest that the cell-binding and PAI-1 binding sequences of Vn occupy distinct regions in the NH2-terminal somatomedin B domain of the molecule.

Detecting distant homologies of mosaic proteins. Analysis of the sequences of thrombomodulin, thrombospondin complement components C9, C8 alpha and C8 beta, vitronectin and plasma cell membrane glycoprotein PC-1.

Patthy L
J Mol Biol. 1988; 202: 689-96

Recognition of homologies may give hints about the structure and function of proteins; therefore, we are developing strategies to aid sequence comparisons. Detecting homology of mosaic proteins is especially difficult since the modules constituting these proteins are usually distantly related and their homology is not readily recognized by conventional computer programs. In the present work we show that the rules of the evolution of mosaic proteins can guide the identification of modules of mosaic proteins and can delineate the group of sequences in which the presence of homologous sequences may be expected. By this approach we can concentrate the search for homology to a limited group of sequences; thus ensuring a more intense and more fruitful search. The power of this approach is illustrated by the fact that it could detect homologies not identified by earlier methods of sequence comparison. In this paper we show that thrombomodulin contains a domain homologous with animal lectins, that complement components C9, C8 alpha and C8 beta have modules homologous with one of the repeat units of thrombospondin and that the somatomedin B module of vitronectin is homologous with the internal repeats of plasma cell membrane glycoprotein PC-1.