Pakistan Research Repository

STUDIES ON THE VENOM OF VIPERIDAE SNAKES (LEAF NOSED VIPER AND HORNED VIPER)

Siddiqui, Abdur Rehman (1991) STUDIES ON THE VENOM OF VIPERIDAE SNAKES (LEAF NOSED VIPER AND HORNED VIPER). PhD thesis, University of Karachi, Karachi.

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Abstract

Snake venom is the secretion of a modified gland, thevenom gland and chemically composed of different enzymic and non-enzymic proteins, beside other organic and in-organic substances. The present study is centered around the phospholipases and protein inhibitors from venoms of Horned viper (Cerastas cerastas) and leaf nosed viper (Eristocophis macmahoni). Most of the present work is carried out on the leaf nosed viper (Eristocophis macmahoni) venom because of the fact that its occurrence is largely limited to the desert areas of Pakistan and Afghanistan. The aim of this study was two fold; 1. Purification and primary structure determination of venom proteins, an effort to understand their structure, function, relationship and biological effects 2. To interpret intra-and inter-species variations in vipers venom proteins by establishing their sequence homology The present study has resulted in purification and characterization of one phospholipase A2 from Horned viper (Cerastas cerastas) venom and two phospholipases A2, one trypsin inhibitor and one platelet aggregation inhibitor from leaf nosed viper (Eristocophis macmahoni) venom Horned viper (Cerastas cerastas) venom phospholipase A2 Phospholipase As has been purification chromatography and reverse phase high performance liquid chromatography. The primary structure has been established by sequence analysis of the intact protein and its Lys-C, Asp-N and Glu-C endoproteases peptides. The structure has 120 amino acid residues, properties like other class IIB phospholipases but only 45-55% identity with the enzyme from other viperid species and large variations even within the species (26% residue differences at known positions in African form). The conserved residues are largely clustered around calcium and catalytic domains. The primary structure also exhibit domains corresponding to anticoagulant effect and myotoxicity Leaf nosed viper (Eristocophis macmahoni) venom phospholipases A2: Two phospholipase A2 isozymes have been purified from leaf nosed viper (Eristocophis macmahoni) by gel filteration chromatography followed by reverse phase HPLC and cation exchange FPLC. Both isozymes contain 7 pairs of hald-cystine, typical of class II phospholipase A2. Surprisingly large differences, affecting both N-and C-terminal regions, exist between the two isozymes purified from the same snake venom. Exchanges occur at no less than 27 of 121 positions (22%) suggesting the possible existence of two genes for phospholipase A2. The residue identity with the enzymes from other viperid species is also low, only 44-48%, indicating extensive variations of this protein structure at large. Functionally, the present isozymes do not possess the cationic regions ascribed to myotoxicity and anti-cogulant effects of the enzyme Leaf nosed viper (Eristocophis macmahoni) venom trypsin inhibitor: A kunitz-type trypsin inhibitor has been purified from the venom of leaf nosed viper, (Eristocophis macmahoni). The primary structure is elucidated by sequence analysis of fragments from endoproteases Lys-C and chymotryptic digests. The polypeptide comprises 62 amino acid residues including six half-Cystines and shows a few residues extended C-terminal. Functionally important residues are conserved with the exception of one residue at both main and weak contact sites. The structure is homologous to known kunitz-type inhibitors from snake venoms and other sources, however closest sequence homology was found with the inhibitor from long nosed viper (73% residue identity) Leaf nosed viper (Eristocophis macmahoni) platelet aggregation inhibitor: Three platelet aggregation inhibitor-type protein have been purified from leaf nosed viper (Eristocophis macmahoni) venom. And the primary structure of major form (Eristocophin) is determined. The Eristocophin is found to contain 62 amino acid residues with 10 half-Cystines. The amino acid sequence of Eristocophin is homologous to other integrin-type proteins characterized from venom of different snake species. It exhibits both RGD-domain and strictly conserved half-Cys residues involved in interaction with integrin receptors Large residue identity is found with other snake venoms platelet aggregation inhibitors. Eristocophin also show residue identity with the RGD-domains of human von willibrand factor and fibronectin A-B

Item Type:Thesis (PhD)
Uncontrolled Keywords:leaf nosed viper, eristocophis macmahoni, horned viper, cerastas cerastas, phospholipases a2, trypsin inhibitor, viperid species
Subjects:Physical Sciences (f) > Chemistry(f2)
ID Code:1416
Deposited By:Mr. Muhammad Asif
Deposited On:26 Mar 2007
Last Modified:04 Oct 2007 21:06

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