serpin family B member 1 (serpin B1), leukocyte elastase inhibitor (LEI)
Leukocyte elastase inhibitor (LEI , also known as proteinase inhibitor 2/PI2, monocyte neutrophil elastase inhibitor/MNEI, EI, or ELANH2) is a member of the clade B serpins or ov-serpins (ovalbumin related serpins) that in humans is encoded by the SERPINB1 gene. Human SERPINB1 is a potent intracellular inhibitor for granzyme H (GzmH) which is constitutively expressed in NK cells and induces target cell death. GzmH cleaves SERPINB1 at Phe343 in the RCL to mediate suicide inhibition. Equine leukocyte elastase inhibitor (HLEI) in contrast to other serpins contains no carbohydrate and has a blocked amino terminus. HLEI is a thymosin beta4-binding protein suggesting a physiological role for cytoplasmic elastase inhibitors in the thymosin B4-regulated rearrangement of the cytoskeleton of leukocytes. HLEI has been proposed to be involved with the control of intracellular protein turnover or the control of elastinolytic activity during inflammation. Ov-serpins are 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.