The serpin SQN-5 is a dual mechanistic-class inhibitor of serine and cysteine proteinases
Biochemistry & Molecular Pharmacology
Biochemistry, Biophysics, and Structural Biology | Life Sciences | Medicine and Health Sciences
SQN-5 is a mouse serpin that is highly similar to the human serpins SCCA1 (SERPINB3) and SCCA2 (SERPINB4). Previous studies characterizing the biochemical activity of SQN-5 showed that this serpin, like SCCA2, inhibited the chymotrypsin-like enzymes mast cell chymase and cathepsin G. Using an expanded panel of papain-like cysteine proteinases, we now show that SQN-5, like SCCA1, inhibited cathepsins K, L, S, and V but not cathepsin B or H. These interactions were characterized by stoichiometries of inhibition that were nearly 1:1 and second-order rate constants of >10(4) M(-1) s(-1). Reactive site loop (RSL) cleavage analysis showed that SQN-5 employed different reactive centers to neutralize the serine and cysteine proteinases. To our knowledge, this is the first serpin that serves as a dual inhibitor of both chymotrypsin-like serine and the papain-like cysteine proteinases by employing an RSL-dependent inhibitory mechanism. The ability of serpins to inhibit both serine and/or papain-like cysteine proteinases may not be a recent event in mammalian evolution. Phylogenetic studies suggested that the SCCA and SQN genes evolved from a common ancestor approximately 250-280 million years ago. When the fact that mammals and birds diverged approximately 310 million years ago is considered, an ancestral SCCA/SQN-like serpin with dual inhibitory activity may be present in many mammalian genomes.
DOI of Published Version
Biochemistry. 2002 Mar 5;41(9):3189-99.
Al-Khunaizi M, Luke CJ, Askew YS, Pak SC, Askew DJ, Cataltepe S, Miller DM, Mills DR, Tsu C, Bromme D, Irving JA, Whisstock JC, Silverman GA. (2002). The serpin SQN-5 is a dual mechanistic-class inhibitor of serine and cysteine proteinases. GSBS Student Publications. https://doi.org/10.1021/bi015999x. Retrieved from https://escholarship.umassmed.edu/gsbs_sp/1627