Differential mode of attack on membrane phospholipids by an acidic phospholipase A 2 (RVVA-PLA 2-I) from Daboia russelli venom

摘要

An acidic phospholipase A 2 (RVVA-PLA 2-I) purified from Daboia russelli venom demonstrated dose-dependent catalytic, mitochondrial and erythrocyte membrane damaging activities. RVVA-PLA 2-I was non-lethal to mice at the tested dose, however, it affected the different organs of mice particularly the liver and cardiac tissues as deduced from the enzymatic activities measured in mice serum after injection of this PLA 2 enzyme. RVVA-PLA 2-I preferentially hydrolyzed phospholipids (phosphatidylcholine) of erythrocyte membrane compared to the liver mitochondrial membrane. Interestingly, RVVA-PLA 2-I failed to hydrolyze membrane phospholipids of HT-29 (colon adenocarcinoma) cells, which contain an abundance of phosphatidylcholine in its outer membrane, within 24 h of incubation. The gas-chromatographic (GC) analysis of saturated/unsaturated fatty acids' release patterns from intact mitochondrial and erythrocyte membranes after the addition of RVVA-PLA 2-I showed a distinctly different result. The results are certainly a reflection of differences in the outer membrane phospholipid composition of tested membranes owing to which they are hydrolyzed by the venom PLA 2s to a different extent. The chemical modification of essential amino acids present in the active site, neutralization study with polyvalent antivenom and heat-inactivation of RVVA-PLA 2-I suggested the correlation between catalytic and membrane damaging activities of this PLA 2 enzyme. Our study advocates that the presence of a large number of PLA 2-sensitive phospholipid domains/composition, rather than only the phosphatidylcholine (PC) content of that particular membrane may determine the extent of membrane damage by a particular venom PLA 2 enzyme.