Abstract
The goal of the present study is to elucidate the effect of lipid domain formation on activities of Naja naja atra and Bungarus multicinctus phospholipase A 2 (PLA 2) enzymes. Sphingomyelin inhibited enzymatic activity and membrane-damaging activity of PLA 2 against egg yolk phosphatidylcholine (EYPC), while cholesterol and cholesterol sulfate abrogated the inhibitory effect of sphingomyelin. The ability of cholesterol and cholesterol sulfate to abolish the inhibitory effect of sphingomyelin was closely related to their capacity to induce domain formation in EYPC/sphingomyelin vesicles. Laurdan fluorescence measurement revealed that membrane packing of EYPC/sphingomyelin vesicles was differently affected by cholesterol and cholesterol sulfate. Unlike cholesterol, cholesterol sulfate was unable to promote domain formation in dipalmitoylphosphatidylcholine (DPPC) vesicles. Cholesterol increased but cholesterol sulfate reduced PLA 2 activity against DPPC. Self-quenching studies and trinitrophenylation of Lys residues revealed that PLA 2 enzymes adopted different membrane-bound mode upon absorption onto the membrane bilayers comprised of different lipid compositions. Collectively, our data indicate that lipid domain formation regulates PLA 2 activity, and suggest that the physical state of membrane bilayers changes the interactive mode of PLA 2 with phospholipids.
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