A particularly labile Asp-Pro bond in the green mamba muscarinic toxin MTX2. Effect of protein conformation on the rate of cleavage.

The single Asp53-Pro54 bond of the MTX2 toxin from the mamba snake Dendroaspis angusticeps is rapidly and efficiently cleaved in acidic solution (pH 1.5-2.5) at 45 degrees C. Unfolding of the toxin slows down the cleavage reaction by several times. Modelling studies indicate that the native toxin conformation can catalyse the Asp53-Pro54 bond cleavage. The implications of this study are: (i) cleavage of Asp-Pro bond for sequence determination may occur better in absence than in presence of denaturant, (ii) mild acid conditions, commonly used in NMR structure determinations, may irreversibly affect the structural integrity of Asp-Pro containing peptides and proteins.