PROTEINASE-INHIBITOR HOMOLOGS AS POTASSIUM CHANNEL BLOCKERS

We report here the NMR structure of dendrotoxin I, a powerful potassiu m channel blocker from the venom of the African Elapidae snake Dendroa spis polylepis polylepis (black mamba), calculated from an experimenta lly-derived set of 719 geometric restraints. The backbone of the toxin superimposes on bovine pancreatic trypsin inhibitor (BPTI) with a roo t-mean-square deviation of <1.7 Angstrom. The surface electrostatic po tential calculated for dendrotoxin I and BPTI, reveal an important dif ference which might account for the differences in function of the two proteins. These proteins may provide examples of adaptation for speci fic and diverse biological functions while at the same time maintainin g the overall three-dimensional structure of a common ancestor.