The role of Pro20 in the isomerization of myotoxin a from Crotalus viridis viridis: folding and structural characterization of synthetic myotoxin a and its Pro20Gly homolog.

Biochemical characterization has established the presence of two conformational forms of myotoxin a. To test the hypothesis that this may be due to cis-trans isomerization at Pro20, synthetic versions of myotoxin a and its Pro20-->Gly structural homolog were folded, then purified using a two-step cation-exchange/reverse-phase perfusion chromatography method. The disulfide bond configuration for the folded proteins was found to be the same as that of native myotoxin a. CE and RPHPLC revealed that folded synthetic myotoxin a exists in two conformations while the Pro20-->Gly homolog exists in only one, supporting the hypothesis that cis-trans isomerization at Pro20 is the source of the myotoxin a conformational heterogeneity.