The Cytosolic Phospholipase A(2)α N-Terminal C2 Domain Binds and Oligomerizes on Membranes with Positive Curvature

Group IV phospholipase A(2)α (cPLA(2)α) regulates the production of prostaglandins and leukotrienes via the formation of arachidonic acid from membrane phospholipids. The targeting and membrane binding of cPLA(2)α to the Golgi involves the N-terminal C2 domain, whereas the catalytic domain produces arachidonic acid. Although most studies of cPLA(2)α concern its catalytic activity, it is also linked to homeostatic processes involving the generation of vesicles that traffic material from the Golgi to the plasma membrane. Here we investigated how membrane curvature influences the homeostatic role of cPLA(2)α in vesicular trafficking. The cPLA(2)α C2 domain is known to induce changes in positive membrane curvature, a process which is dependent on cPLA(2)α membrane penetration. We showed that cPLA(2)α undergoes C2 domain-dependent oligomerization on membranes in vitro and in cells. We found that the association of the cPLA(2)α C2 domain with membranes is limited to membranes with positive curvature, and enhanced C2 domain oligomerization was observed on vesicles ~50 nm in diameter. We demonstrated that the cPLA(2)α C2 domain localizes to cholesterol enriched Golgi-derived vesicles independently of cPLA(2)α catalytic activity. Moreover, we demonstrate the C2 domain selectively localizes to lipid droplets whereas the full-length enzyme to a much lesser extent. Our results therefore provide novel insight into the molecular forces that mediate C2 domain-dependent membrane localization in vitro and in cells.