Crystal Structure of Human Gastric Lipase and Model of Lysosomal Acid Lipase, Two Lipolytic Enzymes of Medical Interest

Alain Roussel,Stéphane Canaan,Marie-Pierre Egloff,Mireille Rivière,Liliane Dupuis,Robert Verger,Christian Cambillau

doi:10.1074/jbc.274.24.16995

Abstract

Fat digestion in humans requires not only the classical pancreatic lipase but also gastric lipase, which is stable and active despite the highly acidic stomach environment. We report here the structure of recombinant human gastric lipase at 3.0-A resolution, the first structure to be described within the mammalian acid lipase family. This globular enzyme (379 residues) consists of a core domain belonging to the alpha/beta hydrolase-fold family and a "cap" domain, which is analogous to that present in serine carboxypeptidases. It possesses a classical catalytic triad (Ser-153, His-353, Asp-324) and an oxyanion hole (NH groups of Gln-154 and Leu-67). Four N-glycosylation sites were identified on the electron density maps. The catalytic serine is deeply buried under a segment consisting of 30 residues, which can be defined as a lid and belonging to the cap domain. The displacement of the lid is necessary for the substrates to have access to Ser-153. A phosphonate inhibitor was positioned in the active site that clearly suggests the location of the hydrophobic substrate binding site. The lysosomal acid lipase was modeled by homology, and possible explanations for some previously reported mutations leading to the cholesterol ester storage disease are given based on the present model.

Highlights

Since 1990, when the first three-dimensional structures of a fungal (Rhizomucor miehei lipase) and a mammalian lipase (human pancreatic lipase (HPL))1 were published, growing interest in lipolysis has led to the structural determination of several lipases of various origins, including those present in bacteria, fungi, and mammals
All the lipases investigated so far vary considerably in size and in their amino acid sequences. They are all serine esterases belonging to the ␣/␤ hydrolase superfamily [1] in which the nucleophilic serine, part of a Ser-His-(Asp/Glu) triad, is located in an extremely sharp turn. Another feature that is common to all the members of the ␣/␤ hydrolase superfamily as well as to proteases is the occurrence of an oxyanion hole, which stabi
The three-dimensional structures of several complexes consisting of lipases bound to covalent inhibitors have been solved: R. miehei lipase [3, 4] and Candida antartica B lipases bound to a C6-alkyl phosphonate [5], Candida rugosa lipase bound to long chain alkyl sulfonyl [6], Pseudomonas cepacia lipase [7] as well as cutinase [8] bound to a dialkylcarbamoylglycerophosphonate, and human pancreatic lipase-colipase complex bound to C11-alkyl phosphonate [9]

Summary

Introduction

Since 1990, when the first three-dimensional structures of a fungal (Rhizomucor miehei lipase) and a mammalian lipase (human pancreatic lipase (HPL))1 were published, growing interest in lipolysis has led to the structural determination of several lipases of various origins, including those present in bacteria, fungi, and mammals. The crystal structure of recombinant HGL at 3.0-Å resolution is determined, and a model of HLAL is discussed and used to possibly explain the previously reported cholesteryl ester storage disease mutations.

Results

Conclusion