Purification, characterization and bactericidal activities of phospholipase A2 from the dromedary intestine

We purified a protein from the dromedary small intestine that displayed potent bactericidal activity against Gram-positive bacteria, and identified it as group-IIA phospholipase A2 (DrPLA2-IIA) by NH2-terminal sequencing and enzymatic measurements. In fact, our findings revealed that the purified PLA2-IIA was a monomeric protein with a molecular mass of about 14 kDa. Pure enzyme has a specific activity of 329 ± 25 U/mg at optimal conditions (pH 9.5 and 45 °C) in the presence of 6 mM NaDC and 7 mM CaCl2 with egg yolk emulsion as substrate and binds with a higher affinity to PE than PS and PC. Furthermore, the DrPLA2-IIA activity was dependent on Ca2+; other cations (Cd2+, Co2+, Fe2+, Mg2+, Mn2+, and Zn2+) reduced the enzymatic activity notably, suggesting that the arrangement of the catalytic site presents an exclusive structure for Ca2+. On the other hand, DrPLA2-IIA was highly bactericidal against Gram-positive bacteria with inhibition zones and IC50 values in the range of 21-27 mm and 3.7-8 μg/ml, respectively, whereas Gram-negative bacteria exhibited a much higher resistance. These observations suggest that the main physiological role of DrPLA2-IIA could be the defense of the intestine against bacterial infections.