title: SjAPI, the first functionally characterized Ascaris-type protease inhibitor from animal venoms.
abstract: BACKGROUND
  Serine protease inhibitors act as modulators of serine proteases, playing important roles in protecting animal toxin peptides from degradation. However, all known serine protease inhibitors discovered thus far from animal venom belong to the Kunitz-type subfamily, and whether there are other novel types of protease inhibitors in animal venom remains unclear.
  
  
  RESULTS
  Here, by screening scorpion venom gland cDNA libraries, we identified the first Ascaris-type animal toxin family, which contains four members: Scorpiops jendeki Ascaris-type protease inhibitor (SjAPI), Scorpiops jendeki Ascaris-type protease inhibitor 2 (SjAPI-2), Chaerilus tricostatus Ascaris-type protease inhibitor (CtAPI), and Buthus martensii Ascaris-type protease inhibitor (BmAPI). The detailed characterization of Ascaris-type peptide SjAPI from the venom gland of scorpion Scorpiops jendeki was carried out. The mature peptide of SjAPI contains 64 residues and possesses a classical Ascaris-type cysteine framework reticulated by five disulfide bridges, different from all known protease inhibitors from venomous animals. Enzyme and inhibitor reaction kinetics experiments showed that recombinant SjAPI was a dual function peptide with α-chymotrypsin- and elastase-inhibiting properties. Recombinant SjAPI inhibited α-chymotrypsin with a Ki of 97.1 nM and elastase with a Ki of 3.7 μM, respectively. Bioinformatics analyses and chimera experiments indicated that SjAPI contained the unique short side chain functional residues "AAV" and might be a useful template to produce new serine protease inhibitors.
  
  
  CONCLUSIONS
  To our knowledge, SjAPI is the first functionally characterized animal toxin peptide with an Ascaris-type fold. The structural and functional diversity of animal toxins with protease-inhibiting properties suggested that bioactive peptides from animal venom glands might be a new source of protease inhibitors, which will accelerate the development of diagnostic and therapeutic agents for human diseases that target diverse proteases.
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Zongyun
authors.initials: Z
authors.lastname: Chen
authors.forename: Bin
authors.initials: B
authors.lastname: Wang
authors.forename: Jun
authors.initials: J
authors.lastname: Hu
authors.forename: Weishan
authors.initials: W
authors.lastname: Yang
authors.forename: Zhijian
authors.initials: Z
authors.lastname: Cao
authors.forename: Renxi
authors.initials: R
authors.lastname: Zhuo
authors.forename: Wenxin
authors.initials: W
authors.lastname: Li
authors.forename: Yingliang
authors.initials: Y
authors.lastname: Wu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002918:Chymotrypsin / Q000737:chemistry / Q000378:metabolism; D015723:Gene Library; D056004:Molecular Dynamics Simulation; D010196:Pancreatic Elastase / Q000737:chemistry / Q000378:metabolism; D010802:Phylogeny; D012604:Scorpion Venoms / Q000737:chemistry*; D016415:Sequence Alignment; D015842:Serine Proteinase Inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D012604:Scorpion Venoms; D015842:Serine Proteinase Inhibitors; D002918:Chymotrypsin; C117608:alpha-chymotrypsin; D010196:Pancreatic Elastase