Crystal Structure of human Lysosomal Acid Lipase and its Implications in Cholesteryl Ester Storage Disease (CESD).

Lysosomal acid lipase (LAL) is a serine hydrolase which hydrolyzes cholesteryl ester and triglycerides delivered to the lysosomes into free cholesterol and fatty acids. LAL deficiency due to mutations in the LAL gene (LIPA) results in accumulation of triglycerides and cholesterol esters in various tissues of the body leading to pathological conditions such as Wolman's disease (WD) and Cholesteryl ester storage disease (CESD). Here we present the first crystal structure of recombinant human LAL to 2.6 A resolution in its closed form. The crystal structure was enabled by mutating three of the six potential glycosylation sites. The overall structure of human LAL (HLAL) closely resembles that of the evolutionarily related human gastric lipase (HGL). It consists of a core domain belonging to the classical α/β hydrolase-fold family with a classical catalytic triad (Ser-153, His-353, Asp-324), an oxyanion hole and a "cap" domain, which regulates substrate entry to the catalytic site. Most significant structural differences between HLAL and HGL exist at the lid region. Deletion of the short helix, 238NLCFLLC244, at the lid region implied a possible role in regulating the highly hydrophobic substrate binding site from self-oligomerization during interfacial activation.  We also performed molecular dynamic simulations of dog gastric lipase (DGL), lid open form and HLAL to gain insights and speculated a possible role of the human mutant, H274Y, leading to CESD.