title: Structural features of a snake venom thrombin-like enzyme: thrombin and trypsin on a single catalytic platform?
abstract: The Lachesis muta thrombin-like enzyme (LM-TL) is a single chain serine protease that shares 38% sequence identity with the serine protease domain of thrombin and also displays similar fibrinogen-clotting activity. In addition, the 228 amino acid residue LM-TL is 52% identical to trypsin, and cleaves chromogenic substrates with similar specificity. Herein we report a three-dimensional (3D) model validated experimentally for LM-TL based on these two homologous proteins of known 3D structure. Spatial modeling of LM-TL reveals a serine protease with a chymotrypsin fold presenting a hydrophobic pocket on its surface, involved in substrate recognition, and an important 90's loop, involved in restricting the LM-TL catalytic site cleft. Docking analysis showed that LM-TL would not form a stable complex with basic pancreatic trypsin inhibitor and wild-type ecotin since its 90's loop would restrict the access to the catalytic site. LM-TL formed acceptable interactions with fibrinopeptide A and a variant of ecotin; ecotin-TSRR/R in which both the primary and secondary binding sites are mutated Val81Thr, Thr83Ser, Met84Arg, Met85Arg and Asp70Arg. Furthermore, analysis of the primary structures of LM-TL and of the seven snake venom thrombin-like enzymes (SVTLEs) family reveals a subgroup formed by LM-TL, crotalase, and bilineobin, both closely related to thrombin. Therefore, LM-TL provides an initial point to compare SVTLEs with their counterparts, e.g. the mammalian serine proteases, and a basis for the localization of important residues within the little known SVTLEs family.
authors: Departamento de Bioquímica Médica-ICB, Universidade Federal do Rio de Janeiro, Brazil. hcastro@bioqmed.ufrj.br
authors: H C
authors: HC
authors: Castro
authors: D M
authors: DM
authors: Silva
authors: C
authors: C
authors: Craik
authors: R B
authors: RB
authors: Zingali
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D003435:Crotalid Venoms / Q000737:chemistry*; D029968:Escherichia coli Proteins; D005340:Fibrinogen / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D033903:Periplasmic Proteins; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D012697:Serine Endopeptidases / Q000737:chemistry; D015842:Serine Proteinase Inhibitors / Q000737:chemistry / Q000235:genetics; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000737:chemistry*; D014357:Trypsin / Q000737:chemistry*; D014361:Trypsin Inhibitors / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D003435:Crotalid Venoms; C039076:Eco protein, E coli; D029968:Escherichia coli Proteins; C072644:Lachesis venom; D033903:Periplasmic Proteins; D015842:Serine Proteinase Inhibitors; D014361:Trypsin Inhibitors; D005340:Fibrinogen; D012697:Serine Endopeptidases; D014357:Trypsin; D013917:Thrombin