A STRUCTURAL HOMOLOG OF COLIPASE IN BLACK MAMBA VENOM REVEALED BY NMRFLOATING DISULFIDE BRIDGE ANALYSIS

The solution structure of mamba intestinal toxin 1 (MIT1), isolated fr om Dendroaspis polylepis polylepis venom, has been determined. This mo lecule is a cysteine-rich polypeptide exhibiting no recognised family membership. Resistance to MIT1 to classical specific endoproteases pro duced contradictory NMR and biochemical information concerning disulph ide-bridge topology. We have used distance restraints allowing ambiguo us partners between S atoms in combination with NMR-derived structural information, to correctly determine the disulphide-bridge topology. T he resultant solution structure of MIT1, determined to a resolution of 0.5 Angstrom, reveals an unexpectedly similar global fold with respec t to colipase, a protein involved in fatty acid digestion. Colipase ex hibits an analogous resistance to endoprotease activity, indicating fo r the first time the possible topological origins of this biochemical property. The biochemical and structural homology permitted us to prop ose a mechanically related digestive function for MIT1 and provides no vel information concerning snake venom protein evolution. (C) 1998 Aca demic Press.