serpin family B member 5, mammary serine proteinase inhibitor
Mammary serine proteinase inhibitor (maspin, also known as proteinase inhibitor 5/PI5), a member of the serpin superfamily, is related to the ov-serpins, with a multitude of effects on cells and tissues at an assortment of developmental stages. Maspin has tumor suppressing activity against breast and prostate cancer. All true inhibitory serpins rely on an exposed reactive center loop (RCL) to inhibit their target proteinase, in which the proteinase cleaves the RCL and becomes incorporated into a serpin-proteinase complex. Maspin differs from other serpins in that its RCL is necessary for activity, but it is not cleaved or rearranged. 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, the RC loop is surface accessible in the active form or buried and inserted as the central beta strand in the inactive form.
Structure:1XQG_A: Human maspin RCL, fully exposed, uncleaved native form
Jiyao W et al.(2023). "The conserved domain database in 2023.",