Chevrier B, Schalk C, D'Orchymont H, Rondeau J M, Moras D, Tarnus C
Laboratoire de Biologie Structurale, Institut de Biologie Moléculaire et Cellulaire, Strasbourg, France.
Structure. 1994 Apr 15;2(4):283-91. doi: 10.1016/s0969-2126(00)00030-7.
Aminopeptidases specifically cleave the amino-terminal residue from polypeptide chains and are involved in the metabolism of biologically active peptides. The family includes zinc-dependent enzymes possessing either one or two zinc ions per active site. Structural studies providing a detailed view of the metal environment may reveal whether the one-zinc and two-zinc enzymes constitute structurally and mechanistically distinct subclasses, and what role the metal ions play in the catalytic process.
We have solved the crystal structure of the monomeric aminopeptidase from Aeromonas proteolytica at 1.8 A resolution. The protein is folded into a single alpha/beta globular domain. The active site contains two zinc ions (3.5 A apart) with shared ligands and symmetrical coordination spheres. We have compared it with the related bovine lens leucine aminopeptidase and the cobalt-containing Escherichia coli methionine aminopeptidase.
The environment and coordination of the two zinc ions in A. proteolytica aminopeptidase strongly support the view that the two metal ions constitute a co-catalytic unit and play equivalent roles during catalysis. This conflicts with the conclusions drawn from the related bovine leucine aminopeptidase and early biochemical studies. In addition, the known specificity of the aminopeptidase for hydrophobic amino-terminal residues is reflected in the hydrophobicity of the active site cleft.
氨肽酶特异性地从多肽链上切割氨基末端残基，并参与生物活性肽的代谢。该家族包括每个活性位点含有一个或两个锌离子的锌依赖性酶。提供金属环境详细视图的结构研究可能揭示单锌和双锌酶是否构成结构和机制上不同的亚类，以及金属离子在催化过程中起什么作用。
我们已解析出解蛋白气单胞菌单体氨肽酶的晶体结构，分辨率为1.8埃。该蛋白质折叠成单个α/β球状结构域。活性位点包含两个锌离子（相距3.5埃），具有共享配体和对称配位球。我们已将其与相关的牛晶状体亮氨酸氨肽酶和含钴的大肠杆菌甲硫氨酸氨肽酶进行了比较。
解蛋白气单胞菌氨肽酶中两个锌离子的环境和配位强烈支持以下观点：这两个金属离子构成一个共催化单元，并在催化过程中发挥同等作用。这与从相关的牛亮氨酸氨肽酶和早期生化研究得出的结论相矛盾。此外，氨肽酶对疏水性氨基末端残基的已知特异性反映在活性位点裂隙的疏水性上。
