Conformational change and inactivation of membrane phospholipid-related activity of cardiotoxin V from Taiwan cobra venom at acidic pH

Cardiotoxin V from Naja naja atra (CTX A5) shows pH-dependence while binding to phosphatidylcholine membrane with pK(sub a) value around 6.0. Proton NMR analysis indicates less CTX A5 relation to membranes at low pH, due to protonation of His-4 near the CTX loop I region's membrane binding site. Due to the influence of pH on pK(sub a), the protonation of His-4 residue also leads to local conformational change in the loop I region, and other amino acid residues in the protein's structural core receive this effect.