title: Amino acid sequences of a heterodimeric neurotoxin from the venom of the false horned viper (Pseudocerastes fieldi).
abstract: The main toxic component of the venom of the false horned viper, Pseudocerastes fieldi, is a heterodimeric neurotoxin composed of a basic subunit, Cb II, and one of two acidic subunits, either Cb I alpha or Cb I beta. The nontoxic acidic subunit increases the toxicity of the basic subunit. Both subunits have phospholipase A2 (PLA2) amino acid sequences. Cb I alpha and Cb I beta themselves are inactive towards phosphatidylcholine and when complexed with Cb II promote a delay in the onset of phospholipase activity of Cb II. Cb I alpha and Cb I beta do hydrolyze the synthetic substrate, 3-octanoyloxy-4-nitrobenzoic acid, but at < 1% the rate of Cb II. Comparisons of the amino acid sequences of Cb II and Cb I alpha with the corresponding acidic and basic subunits of other heterodimeric neurotoxins show high amino acid sequence identity. Some of the amino acids which are different between the acidic and basic subunits are in highly conserved sequences in their respective types of PLA2. This suggests that these amino acid changes in the conserved regions are important for the structure and function of the heterodimeric proteins.
authors.affiliation: Department of Molecular Biology, University of Wyoming, Laramie 82071, USA.
authors.forename: B
authors.initials: B
authors.lastname: Francis
authors.forename: A
authors.initials: A
authors.lastname: Bdolah
authors.forename: I I
authors.initials: II
authors.lastname: Kaiser
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D009498:Neurotoxins / Q000737:chemistry / Q000302:isolation & purification*; D010740:Phospholipases / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D014757:Viper Venoms / Q000737:chemistry / Q000201:enzymology / Q000302:isolation & purification*
chemical_list: D009498:Neurotoxins; D014757:Viper Venoms; D010740:Phospholipases