title: Crotalase, a fibrinogen-clotting snake venom enzyme: primary structure and evidence for a fibrinogen recognition exosite different from thrombin.
abstract: Crotalase, a fibrinogen-clotting enzyme isolated from the venom of Crotalus adamanteus, and its overlapping fragments were subjected to Edman degradation. The resulting amino acid sequence [see text] characteristic of a serine proteinase. Comparison with thrombin, the physiological fibrinogen-clotting enzyme, showed that thrombin's fibrinogen-recognition exosite (FRE) is poorly represented in crotalase. Hirudin, a FRE-dependent inhibitor, had no effect on crotalase. Spatial modeling of crotalase yielded a possible alternative fibrinogen-recognition site comprised of Arg 60F, Lys 85, Lys 87, and Arg 107 (underlined in the sequence above). Crotalase also lacks thrombin's YPPW loop, as well as its functionally important ETW 146-148, and its heparin-binding site. The enzyme contains a single asparagine-linked glycosylation site, NFT, bearing neutral and amino sugars that account for 8.3% of the enzyme's total molecular weight of 29,027. The calculated absorbance of crotalase at 280 nm, 1%, cm(-1) is 15.2.
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine 92697, USA.
authors.forename: A H
authors.initials: AH
authors.lastname: Henschen-Edman
authors.forename: I
authors.initials: I
authors.lastname: Theodor
authors.forename: B F
authors.initials: BF
authors.lastname: Edwards
authors.forename: H
authors.initials: H
authors.lastname: Pirkle
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D003435:Crotalid Venoms; D017839:Crotalus; D004789:Enzyme Activation; D005340:Fibrinogen / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment; D017421:Sequence Analysis; D012697:Serine Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013917:Thrombin / Q000378:metabolism*
chemical_list: D003435:Crotalid Venoms; D005340:Fibrinogen; D012697:Serine Endopeptidases; D013917:Thrombin; C019948:crotalase