Structure and Function of Lysosomal Phospholipase A2 and Lecithin:Cholesterol Acyltransferase.

[摘要] Lysosomal phospholipase A2 (LPLA2) and lecithin:cholesterol acyltransferase (LCAT) belong to a structurally uncharacterized family of lipid metabolizing enzymes responsible for lung surfactant catabolism and reverse cholesterol transport, respectively. Whereas LPLA2 is predicted to underlie the development of drug-induced phospholipidosis, somatic mutations in LCAT cause familial LCAT deficiency (FLD). Herein are described multiple high resolution crystal structures of human LPLA2 and a low resolution structure of LCAT that confirms its close structural relationship to LPLA2. Insertions in the α/β hydrolase core of LPLA2 form domains with unique folds that are responsible for membrane interaction and binding the acyl chains and head groups of phospholipid substrates. The wide opening of the LPLA2 active site faces the membrane for an easy access to glycerophospholipids and lipophilic alcohols, its preferred substrates. Based on these structures, substrate modeling, and the position of disease-causing mutations in LCAT, we propose that orientation of the bound phospholipid in the active site underlies the specificity of LPLA2 for fatty acids in the sn-2 vs. sn-1 position, and that preference for length of the acyl chains is dictated by two hydrophobic grooves leading away from the catalytic triad of the enzyme. We proposed a 2-step mechanism for LPLA2 membrane binding, consisting of a transient LPLA2 interaction with the membrane via its surface hydrophobic residues. High-affinity membrane interaction occurs through the bound substrate and the catalytic intermediate. Based on LPLA2 structure we built an LCAT homology model and validated it by solving the 8.7 Å structure of LCAT. Then we used this model to map known genetic LCAT mutations leading to either fish eye disease (FED) or FLD. We determined that most FLD-causing mutations result in either structural defects or catalytic impairments. On the other hand, FED mutations mostly cluster on the surface of the hydrolase domain and might define a surface for LCAT interactions with apolipoprotein A (ApoA)-I, a key component of HDL. The LCAT structure thus paves the way for rational development of new therapeutics to treat FLD, atherosclerosis, and acute coronary syndrome.

[发布机构] University of Michigan

[效力级别] triacylglycerol lipase

[关键词] Structure and Function of Lysosomal Phospholipase A2 and Lecithin:Cholesterol Acyltransferase;triacylglycerol lipase;phospholipase;α/β hydrolase fold;interfacial activation;transacylase;PLA2;LPLA2;LCAT;LCAT-like lysophospholipase;LLPL;N-glycosylation;phospholipidosis;transesterification;reverse cholesterol transport;fish eye disease;FED;FLD;familial LCAT deficiency;crystallography;selenomethionine labeling;GRK;G protein-coupled receptor kinases;GRK5;calmodulin;CaM;Biological Chemistry;Science (General);Science;Chemical Biology