Teplyakov A, Polyakov K, Obmolova G, Strokopytov B, Kuranova I, Osterman A, Grishin N, Smulevitch S, Zagnitko O, Galperina O
European Molecular Biology Laboratory, Hamburg, Federal Republic of Germany.
Eur J Biochem. 1992 Sep 1;208(2):281-8. doi: 10.1111/j.1432-1033.1992.tb17184.x.
The crystal structure of carboxypeptidase T from Thermoactinomyces vulgaris has been determined at 0.235-nm resolution by X-ray diffraction. Carboxypeptidase T is a remote homologue of mammalian Zn-carboxypeptidases. In spite of the low degree of amino acid sequence identity, the three-dimensional structure of carboxypeptidase T is very similar to that of pancreatic carboxypeptidases A and B. The core of the protein molecule is formed by an eight-stranded mixed beta sheet. The active site is located at the C-edge of the central (parallel) part of the beta sheet. The structural organization of the active centre appears to be essentially the same in the three carboxypeptidases. Amino acid residues directly involved in catalysis and binding of the C-terminal carboxyl of a substrate are strictly conserved. This suggests that the catalytic mechanism proposed for the pancreatic enzymes is applicable to carboxypeptidase T and to the whole family of Zn-carboxypeptidases. Comparison of the amino acid replacements at the primary specificity pocket of carboxypeptidases A, B and T provides an explanation of the unusual 'A+B' type of specificity of carboxypeptidase T. Four calcium-binding sites localized in the crystal structure of carboxypeptidase T could account for the high thermostability of the protein.
通过X射线衍射，已在0.235纳米分辨率下测定了嗜热放线菌羧肽酶T的晶体结构。羧肽酶T是哺乳动物锌羧肽酶的远亲同源物。尽管氨基酸序列同一性程度较低，但羧肽酶T的三维结构与胰腺羧肽酶A和B的结构非常相似。蛋白质分子的核心由一个八链混合β折叠片层构成。活性位点位于β折叠片层中央（平行）部分的C边缘。在这三种羧肽酶中，活性中心的结构组织似乎基本相同。直接参与催化和底物C末端羧基结合的氨基酸残基严格保守。这表明为胰腺酶提出的催化机制适用于羧肽酶T以及整个锌羧肽酶家族。对羧肽酶A、B和T的主要特异性口袋处氨基酸置换的比较，解释了羧肽酶T不寻常的“A + B”型特异性。羧肽酶T晶体结构中定位的四个钙结合位点可以解释该蛋白质的高热稳定性。
