serpin family A member 16, HongrES1 and similar proteins
HongrES1 is an epididymis-specific secretory protein and is encoded by the SERPINA16 gene. It is one of several potential decapacitation factors of rodents, including a 40-kDa glycoprotein, phosphatidylethanolamine-binding protein 1 (PEBP1), a cysteine-rich secretory protein 1, an acrosome-stabilizing factor, SVA, SVS2, and SPINKL. In humans, some potential decapacitation factors that have been reported are glycodelin-S, semenogelin I, a 130-kDa glycoprotein, and some mannosyl glycopeptides. Decapitation factors are removed from the sperm head surface during the capacitation process and are able to reverse sperm capacitation. The clade A of the serpin superfamily includes the classical serine proteinase inhibitors, alpha-1-antitrypsin and alpha-1-antichymotrypsin, protein C inhibitor, kallistatin, and non-inhibitory serpins, like corticosteroid and thyroxin binding globulins. In general, SERine Proteinase INhibitors (serpins) exhibit conformational polymorphism shifting from native to cleaved, latent, delta, or polymorphic forms. Many serpins, such as antitrypsin and antichymotrypsin, function as serine protease inhibitors which regulate blood coagulation cascades. Non-inhibitory serpins perform many diverse functions such as chaperoning proteins or transporting hormones. Serpins are of medical interest because mutants have been associated with blood clotting disorders, emphysema, cirrhosis, and dementia. A classification based on evolutionary relatedness has resulted in the assignment of serpins to 16 clades designated A-P along with some orphans.
Comment:depending on the conformational state, the RC loop is surface accessible in the active form or buried and inserted as the central beta strand in the inactive form.
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