serpin family B members 3 and 4, squamous cell carcinoma antigens 1 and 2
Squamous cell carcinoma antigen 1 (SCCA1, also called HsT1196 or protein T4-A) and squamous cell carcinoma antigen 2 (SCCA2, also called PI11 or leupin), which are encoded by the SERPINB3 and SERPINB4 genes, respectively, are members of the serpin family of serine protease inhibitors. SCCA1 is a so called cross-class serpin, inhibiting cysteine proteinases such as cathepsin S, K, L, and papain. SCCA2 inhibits chymotrypsin-like serine proteases including chymase, cathepsin G, and Der p1. Elevated levels of SCCA1 and SCCA2 have been detected in chronic inflammatory conditions involving the skin, especially atopic dermatitis (AD)and psoriasis, as well as in respiratory inflammatory diseases such as asthma, chronic obstructive pulmonary disease (COPD), and tuberculosis. They are both normally co-expressed in squamous epithelial cells of tongue, esophagus, tonsils, epidermal hair follicles, lung and uterus, and become highly up-regulated in squamous carcinomas of these organs. Diseases associated with SERPINB3 include anal cancer and cervical squamous cell carcinoma, whereas SERPINB4 include squamous cell carcinoma and chromosome 18Q deletion syndrome. The ovalbumin family of serpins (ov-serpins) is a family of closely related proteins, whose members can be secreted (ovalbumin), cytosolic (leukocyte elastase inhibitor, LEI), or targeted to both compartments (plasminogen activator inhibitor 2, PAI-2). It also characterized by N- and C-terminal extensions, the absence of a signal peptide, and a Ser rather than an Asn residue at the penultimate position. The ov-serpins corresponds to clade B of the serpin superfamily. 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 can cause 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, RCL is surface accessible in the active form or buried and inserted as the central beta strand in the inactive form
Structure:4ZK3_A: Human Pso p27, generated by cleavage of serpinB3, RCL, inserted
Structure:2ZV6_A: Human SCCA1 (serpinB3) RCL, flexible and solvent exposed
Jiyao W et al.(2023). "The conserved domain database in 2023.",