Recent progress in understanding the diversity of the human ov-serpin/clade B serpin family

The inhibitory mechanism against proteases is important in the maintenance of homeostasis or health in the body. The human ovalbumin serpin (ovserpin)/ clade B serpin family is one group of the human serpins, a family of serine protease inhibitors. They have acquired diversity in the profiles of target proteases, inhibitory mechanisms, and localization patterns during their evolution. Most serpins target serine proteases, however, some ov-serpins target only cysteine proteases or both serine and cysteine proteases and furthermore, several ov-serpins do not possess inhibitory activities. Although the ov-serpins act primarily as intracellular serpins, some show extracellular and nuclear localizations. Such diversity enables the ov-serpins to play multiple physiological roles in the body. Recent analyses have revealed that the functions of human ov-serpins are more diversified than we previously knew. In this article, we describe recent progress in our understanding of how the human ov-serpin/clade B serpin family demonstrates diversity.     

Human clade B serpins (ov-serpins) belong to a cohort of evolutionarily dispersed <Emphasis Type="Italic">intracellular</Emphasis> proteinase inhibitor clades that protect cells from promiscuous proteolysis

Serpins are unique among the various types of active site proteinase inhibitors because they covalently trap their targets by undergoing an irreversible conformational rearrangement. Members of the serpin superfamily are present in the three major domains of life (Bacteria, Archaea and Eukarya) as well as several eukaryotic viruses. The human genome encodes for at least 35 members that segregate evolutionarily into nine (A-I) distinct clades. Most of the human serpins are secreted and circulate in the bloodstream where they reside at critical checkpoints intersecting self-perpetuating proteolytic cascades such as those of the clotting, thrombolytic and complement systems. Unlike these circulating serpins, the clade B serpins (ov-serpins) lack signal peptides and reside primarily within cells. Most of the human clade B serpins inhibit serine and/or papain-like cysteine proteinases and protect cells from exogenous and endogenous proteinase-mediated injury. Moreover, as sequencing projects expand to the genomes of other species, it has become apparent that intracellular serpins belonging to distinct phylogenic clades are also present in the three major domains of life. As some of these serpins also guard cells against the deleterious effects of promiscuous proteolytic activity, we propose that this cytoprotective function, along with similarities in structure are common features of a cohort of intracellular serpin clades from a wide variety of species.Received 24 June 2003; received after revision 16 July 2003; accepted 5 August 2003