The cytosolic phospholipase A2 catalytic domain modulates association and residence time at Golgi membranes

Cytosolic phospholipase A(2) (cPLA(2)) catalyzes release of arachidonic acid from membranes following translocation to Golgi and endoplasmic reticulum. In response to an intracellular calcium concentration ([Ca2+](i)) increase, the C2 domain binds Ca2+ and brings the catalytic domain into proximity with its phospholipid substrate. Because membrane residence is important in the regulation of cPLA(2) activity, we explored the contributions of the C2 and catalytic domains in mediating membrane residence using an imaging approach in live cells with fluorescent protein chimeras of cPLA(2). The isolated cPLA(2) C2 domain associated with Golgi membranes rapidly in proportion to the [Ca2+](i), allowing for its use as a [Ca2+](i) indicator. cPLA(2) association with Golgi was slower than the isolated C2 domain in response to a [Ca2+](i) increase. After [Ca2+](i) decrease, cPLA(2) remained associated with membrane in a Ca2+-independent fashion whereas C2 domain rapidly dissociated. Ca2+-independent membrane association was greatly reduced by mutation of Trp(464), located at the membrane-exposed face of the catalytic domain, to Gly or Ala. Mutation of Trp(464) to Phe supported Ca2+-independent association similar to wild type. These results demonstrate a role for the cPLA(2) catalytic domain in regulating membrane association and membrane residence time.