文章基本信息

标题：Three-dimensional structure of phosphoenolpyruvate carboxylase: A proposed mechanism for allosteric inhibition
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作者：Yasushi Kai ; Hiroyoshi Matsumura ; Tsuyoshi Inoue 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1999
卷号：96
期号：3
页码：823-828
DOI：10.1073/pnas.96.3.823
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The crystal structure of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) has been determined by x-ray diffraction methods at 2.8-A resolution by using Escherichia coli PEPC complexed with L-aspartate, an allosteric inhibitor of all known PEPCs. The four subunits are arranged in a "dimer-of-dimers" form with respect to subunit contact, resulting in an overall square arrangement. The contents of -helices and {beta}-strands are 65% and 5%, respectively. All of the eight {beta}-strands, which are widely dispersed in the primary structure, participate in the formation of a single {beta}-barrel. Replacement of a conserved Arg residue (Arg-438) in this linkage with Cys increased the tendency of the enzyme to dissociate into dimers. The location of the catalytic site is likely to be near the C-terminal side of the {beta}-barrel. The binding site for L-aspartate is located about 20 A away from the catalytic site, and four residues (Lys-773, Arg-832, Arg-587, and Asn-881) are involved in effector binding. The participation of Arg-587 is unexpected, because it is known to be catalytically essential. Because this residue is in a highly conserved glycine-rich loop, which is characteristic of PEPC, L-aspartate seemingly causes inhibition by removing this glycine-rich loop from the catalytic site. There is another mobile loop from Lys-702 to Gly-708 that is missing in the crystal structure. The importance of this loop in catalytic activity was also shown. Thus, the crystal-structure determination of PEPC revealed two mobile loops bearing the enzymatic functions and accompanying allosteric inhibition by L-aspartate.