Interfacial enzymology of parvovirus phospholipases A2.

The capsid of parvoviruses proteins were recently shown to contain secreted phospholipase A(2) (sPLA(2))-like activity that is required during host cell entry. Parvoviral PLA(2) domains have little sequence identity with sPLA(2)s and lack disulfide bonds. In the present study, after bacterial expression and purification, the biochemical characterizations of these first PLA(2)s identified in viruses have been investigated, and a comparison has been made with other known PLA(2)s. The specific activities of three viral PLA(2)s differed by 3 orders of magnitude, with porcine parvovirus PLA(2) displaying a specific activity similar to that of the most active sPLA(2)s (e.g. human group IIA) and the human AAV2 and B19 parvoviral enzymes displaying approximately 10(3) lower specific activities (similar to human sPLA(2) groups IIE and XIIA). These differences were not caused by weaker Ca(2+) or interfacial binding. The specific activities of the viral PLA(2)s on zwitterionic or anionic phospholipid vesicles were comparable. The viral PLA(2)s did not display a preference for unsaturated versus saturated sn-2 fatty acyl chains and hydrolyzed all major classes of glycero-phospholipids except phosphatidylinositol. Incubation of mammalian cells with porcine parvovirus PLA(2) led to the release of arachidonic acid into the culture medium. Interestingly, among nine previously known sPLA(2) inhibitors, only a subset showed inhibition of the viral PLA(2)s and with weak potency, indicating that the active sites of these new enzymes are structurally distinct from those of sPLA(2)s. Based on these distinct enzymatic and structural properties, we propose to classify the parvovirus PLA(2)s within the PLA(2) superfamily as group XIII enzymes.