Miled N, Canaan S, Dupuis L, Roussel A, Rivière M, Carrière F, de Caro A, Cambillau C, Verger R
Laboratoire de Lipolyse Enzymatique, CNRS-IFR1 UPR 9025, 31, chemin Joseph-Aiguier, 13402 cedex 20, Marseille, France.
Biochimie. 2000 Nov;82(11):973-86. doi: 10.1016/s0300-9084(00)01179-2.
Human gastric lipase (HGL) is a lipolytic enzyme that is secreted by the chief cells located in the fundic part of the stomach. HGL plays an important role in lipid digestion, since it promotes the subsequent hydrolytic action of pancreatic lipase in duodenal lumen. Physiological studies have shown that HGL is able of acting not only in the highly acid stomach environment but also in the duodenum in synergy with human pancreatic lipase (HPL). Recombinant HGL (r-HGL) was expressed in the baculovirus/insect cell system in the form of an active protein with a molecular mass of 45 kDa. The specific activities of r-HGL were found to be similar to that of the native enzyme when tested on various triacylglycerol (TG) substrates. The 3-D structure of r-HGL was the first solved within the mammalian acid lipase family. This globular enzyme (379 residues) shows a new feature, different from the other known lipases structures, which consists of a core domain having the alpha/beta hydrolase fold and a cap domain including a putative 'lid' of 30 residues covering the active site of the lipase (closed conformation). HPL is the major lipolytic enzyme involved in the digestion of dietary TG. HPL is a 50 kDa glycoprotein which is directly secreted as an active enzyme. HPL was the first mammalian lipase to be solved structurally, and it revealed the presence of two structural domains: a large N-terminal domain (residues 1-336) and a smaller C-terminal domain (residues 337-449). The large N-terminal domain belongs to the alpha/beta hydrolase fold and contains the active site. A surface loop called the lid domain (C237-C261) covers the active site in the closed conformation of the lipase. The 3-D structure of the lipase-procolipase complex illustrates how the procolipase might anchor the lipase at the interface in the presence of bile salts: procolipase binds to the C-terminal domain of HPL and exposes the hydrophobic tips of its fingers at the opposite site of its lipase-binding domain. These hydrophobic tips help to bring N-terminal domain into close conformation with the interface where the opening of the lid domain probably occurs. As a result of all these conformational changes, the open lid and the extremities of the procolipase form an impressive continuous hydrophobic plateau, extending over more than 50 A. This surface might able to interact strongly with a lipid-water interface. The biochemical, histochemical and clinical studies as well as the 3-D structures obtained will be a great help for a better understanding of the structure-function relationships of digestive lipases.
人胃脂肪酶（HGL）是一种脂解酶，由位于胃底部的主细胞分泌。HGL在脂质消化中起重要作用，因为它促进十二指肠腔内胰脂肪酶的后续水解作用。生理学研究表明，HGL不仅能够在高度酸性的胃环境中发挥作用，还能与人类胰脂肪酶（HPL）协同作用于十二指肠。重组HGL（r-HGL）在杆状病毒/昆虫细胞系统中以分子量为45 kDa的活性蛋白形式表达。当在各种三酰甘油（TG）底物上进行测试时，发现r-HGL的比活性与天然酶相似。r-HGL的三维结构是哺乳动物酸性脂肪酶家族中第一个解析出来的。这种球状酶（379个残基）呈现出一个不同于其他已知脂肪酶结构的新特征，它由具有α/β水解酶折叠的核心结构域和一个包含覆盖脂肪酶活性位点的30个残基的假定“盖子”的帽结构域组成（闭合构象）。HPL是参与膳食TG消化的主要脂解酶。HPL是一种50 kDa的糖蛋白，直接作为活性酶分泌。HPL是第一个在结构上得到解析的哺乳动物脂肪酶，它揭示了两个结构域的存在：一个大的N端结构域（残基1-336）和一个较小的C端结构域（残基337-449）。大的N端结构域属于α/β水解酶折叠，包含活性位点。一个称为盖子结构域（C237-C261）的表面环在脂肪酶的闭合构象中覆盖活性位点。脂肪酶-前脂肪酶复合物的三维结构说明了在前脂肪酶存在的情况下，前脂肪酶如何在胆汁盐存在时将脂肪酶锚定在界面上：前脂肪酶与HPL的C端结构域结合，并在其脂肪酶结合结构域的相反位点暴露其手指状结构的疏水末端。这些疏水末端有助于使N端结构域与可能发生盖子结构域打开的界面紧密构象。由于所有这些构象变化，开放的盖子和前脂肪酶的末端形成了一个令人印象深刻的连续疏水平台，延伸超过50埃。这个表面可能能够与脂质-水界面强烈相互作用。所进行的生化、组织化学和临床研究以及获得的三维结构将极大地有助于更好地理解消化脂肪酶的结构-功能关系。
