title: A new type of thrombin inhibitor, noncytotoxic phospholipase A2, from the Naja haje cobra venom.
abstract: Thrombin is a key enzyme in the blood coagulation cascade and is also involved in carcinogenesis; therefore, its inhibitors are of fundamental and clinical importance. Snake venoms are widely used as sources of proteins that affect blood coagulation. We have isolated a new protein, called TI-Nh, from the Naja haje cobra venom. TI-Nh is a mixed-type inhibitor of thrombin (K(i) of 72.8 nM for a synthetic peptide substrate) and effectively inhibits thrombin-induced platelet aggregation with an IC(50) value of 0.2 nM. At concentrations up to approximately 50 nM, at which the thrombin-clotting time is substantially prolonged, TI-Nh exerts no detectable effects on both the intrinsic and extrinsic pathways of the coagulation cascade. It does not hydrolyze either fibrinogen or thrombin. Although TI-Nh bears structural features typical of group IB phospholipases A(2) (PLA(2)s), it possesses relatively weak enzymatic activity and is nontoxic to PC12 cells at concentrations up to 15 microM. Nevertheless, TI-Nh evokes neurite outgrowth in these cells at a concentration of approximately 1 microM, similar to cytotoxic snake PLA(2)s with strong enzymatic activity. TI-Nh is the first thrombin inhibitor found in the venom of the Elapidae snake family, and it is the first phospholipase shown to inhibit thrombin.
authors.affiliation: Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, ul. Miklukho-Maklaya 16/10, Moscow V-437, 117997 GSP, Russian Federation.
authors.forename: Alexey V
authors.initials: AV
authors.lastname: Osipov
authors.forename: Sergey Yu
authors.initials: SY
authors.lastname: Filkin
authors.forename: Yana V
authors.initials: YV
authors.lastname: Makarova
authors.forename: Victor I
authors.initials: VI
authors.lastname: Tsetlin
authors.forename: Yuri N
authors.initials: YN
authors.lastname: Utkin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001777:Blood Coagulation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003165:Complement System Proteins / Q000187:drug effects; D003890:Desiccation; D004534:Egypt; D004546:Elapid Venoms / Q000737:chemistry / Q000201:enzymology* / Q000494:pharmacology*; D015942:Factor VIIa / Q000037:antagonists & inhibitors; D005337:Fibrin / Q000737:chemistry; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016501:Neurites / Q000187:drug effects; D054467:Phospholipases A2 / Q000494:pharmacology*; D010974:Platelet Aggregation / Q000187:drug effects; D011506:Proteins / Q000737:chemistry; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013917:Thrombin / Q000037:antagonists & inhibitors*; D013925:Thromboplastin / Q000037:antagonists & inhibitors; D014361:Trypsin Inhibitors / Q000494:pharmacology; D014914:Whole Blood Coagulation Time
chemical_list: D004546:Elapid Venoms; D011506:Proteins; D015842:Serine Proteinase Inhibitors; D014361:Trypsin Inhibitors; D005337:Fibrin; D003165:Complement System Proteins; D013925:Thromboplastin; D054467:Phospholipases A2; D015942:Factor VIIa; D013917:Thrombin