Abstract
Lysosomal acid lipase (LAL) is a serine hydrolase that hydrolyzes cholesteryl ester (CE) and TGs delivered to the lysosomes into free cholesterol and fatty acids. LAL deficiency due to mutations in the LAL gene (LIPA) results in accumulation of TGs and cholesterol esters in various tissues of the body leading to pathological conditions such as Wolman’s disease and CE storage disease (CESD). Here, we present the first crystal structure of recombinant human LAL (HLAL) to 2.6 Å resolution in its closed form. The crystal structure was enabled by mutating three of the six potential glycosylation sites. The overall structure of 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 (lid-open form) and HLAL to gain insights and speculated a possible role of the human mutant, H274Y, leading to CESD.
Highlights
Lysosomal acid lipase (LAL) is a serine hydrolase that hydrolyzes cholesteryl ester (CE) and TGs delivered to the lysosomes into free cholesterol and fatty acids
Lysosomal acid lipase (LAL) is a serine hydrolase enzyme located in the lysosome, where it breaks down cholesteryl esters (CEs) and TGs into free cholesterol and fatty acids [1,2,3]
Sequence alignment of LAL isoforms from human, monkey, mouse, and rat revealed five putative glycosylation sites (Asn-15, Asn-80, Asn-140, Asn-252, and Asn-300; mature protein numbering) that are highly conserved among all species, while a sixth site (Asn-51) is present only in human and monkey (Fig. 1)
Summary
Lysosomal acid lipase (LAL) is a serine hydrolase that hydrolyzes cholesteryl ester (CE) and TGs delivered to the lysosomes into free cholesterol and fatty acids. The overall structure of HLAL closely resembles that of the evolutionarily related human gastric lipase (HGL). It consists of a core domain belonging to the classical / 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. The gene (LIPA) that encodes HLAL was mapped on chromosome 10q23.2-q23.3, and it consists of 10 exons spread over 36 kb DNA [16] It shares 58% and 57% amino acid identity with human gastric lipase (HGL) and rat lingual lipase (RLL), respectively [4]. Alanine substitution of Cys-227 and Cys-336, alone or together, has significantly reduced hydrolase activity in a substrate-dependent manner, while the other Cys mutants did not drastically affect activity [19]
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