van Tilbeurgh H, Roussel A, Lalouel J M, Cambillau C
Laboratory of Cristallisation et Macromolecules Biologiques-Centre National de la Recherche Scientifique, Faculté de Médecine Nord, Marseille, France.
J Biol Chem. 1994 Feb 11;269(6):4626-33.
Lipoprotein lipase and pancreatic lipase have about 30% sequence identity, suggesting a similar tertiary fold. Three-dimensional models of lipoprotein lipase were constructed, based upon two recently determined x-ray crystal structures of pancreatic lipase, in which the active site was in an open and closed conformation, respectively. These models allow us to propose a few hypotheses on the structural determinants of lipoprotein lipase which are responsible for heparin binding, dimer formation, and phospholipase activity. The folding of the protein assembles a number of positive charge clusters at the back of the molecule, opposite the active site. These clusters probably form the heparin binding site, as confirmed by recent site-directed mutagenesis experiments. The active sites of lipoprotein lipase and pancreatic lipase look very similar, except for the lid (a surface loop covering the catalytic serine in the inactive state). A different open (active) conformation of the lid in both enzymes may be responsible for their differing substrate specificities. Predictions of the nature of the lipoprotein lipase dimer remain elusive, although our model enabled us to propose a few possibilities.
脂蛋白脂肪酶和胰脂肪酶具有约30%的序列同一性，这表明它们具有相似的三级结构。基于最近确定的胰脂肪酶的两个X射线晶体结构构建了脂蛋白脂肪酶的三维模型，其中活性位点分别处于开放和闭合构象。这些模型使我们能够对脂蛋白脂肪酶的结构决定因素提出一些假设，这些因素负责肝素结合、二聚体形成和磷脂酶活性。蛋白质的折叠在分子背面与活性位点相对的位置组装了许多正电荷簇。这些簇可能形成肝素结合位点，最近的定点诱变实验证实了这一点。脂蛋白脂肪酶和胰脂肪酶的活性位点看起来非常相似，除了盖子（在无活性状态下覆盖催化丝氨酸的表面环）。两种酶中盖子不同的开放（活性）构象可能是它们不同底物特异性的原因。尽管我们的模型使我们能够提出一些可能性，但脂蛋白脂肪酶二聚体性质的预测仍然难以捉摸。
