Sterol and steryl ester regulation of phospholipase A₂ from the mosquito parasiteLagenidium giganteum

Abstract

Lagenidium giganteum, a facultative parasite of mosquito larvae, cannot synthesize sterols, and requires an exogenous source of these lipids in order to enter its reproductive cycle. This parasite grows vegetatively in the absence of sterols, but requires cholesterol or structurally related compounds to produce motile zoospores, which are the only stage capable of infecting mosquitoes. Sterols structurally related to cholesterol and some steryl esters inhibited the activity of L. giganteum phospholipase A2 (PLA2), an enzyme that hydrolyzes fatty acids from the sn-2 position of glycerophospholipids. Sterols that induce reproduction inhibited L. giganteum PLA2 activity, while sterols and steroids that do not support sporulation had minimal effect. Most steryl esters had no effect on enzyme activity, but cholesteryl arachidonate (CA) was a potent inhibitor of parasite PLA2. Not all enzymes partly purified using a DEAE-Sephacel column were affected by these lipids, demonstrating selective inhibition of specific enzymes. Potency was enhanced by up to several orders of magnitude if epoxy fatty acids were esterified to the cholesterol nucleus. The steryl ester pool was dynamic during morphogenesis, and the fatty acid composition of the steryl esters did not mimic total cell or membrane (glycerophospholipid) fatty acid composition as L. giganteum proceeded through its growth cycle. Synthesis of CA and monoepoxy CA by the parasite was confirmed using electrospray mass spectrometry and collision-induced dissociation. Steryl derivatives selectively inhibited PLA2 enzymes from bovine pancreas, snake venom, and human cytoplasmic 85-kDa PLA2.

Phospholipase A2-Induced Remodeling Processes on Liquid-Ordered/Liquid-Disordered Membranes Containing Docosahexaenoic or Oleic Acid: A Comparison Study

“…The addition of chol to both types of PCs (PCs/chol: 80/20, 66/34, and 50/50 mol/mol) also exerted an inhibitory effect on the activity of the PLA 2 (Figure ). This result is in agreement with the work of Kerwin et al, who reported that sterol and steryl derivatives selectively inhibited PLA 2 from bovine pancreas, snake venom, and human cytoplasmic 85-kDa PLA 2 . Cholesterol induced a concentration-dependent inhibition of PLA 2 activity in POPC/chol mixtures where the enzymatic activity was decreased to 73%, 40%, and 24% at 150, 300, and 600 nmol chol, respectively.…”