Human mitochondrial branched chain aminotransferase: structural basis for substrate specificity and role of redox active cysteines
Human mitochondrial branched chain aminotransferase: structural basis for substrate specificity and role of redox active cysteines
复制标题
DOI：
10.1016/s1570-9639(03)00051-7
复制
发表时间：
2003-04-11
影响因子：
3.2
通讯作者：
Hutson, SM
中科院分区：
文献类型：
--
作者：
Conway, ME;Yennawar, N;Hutson, SM
折叠IV型磷酸吡哆醛（PLP）依赖性人线粒体支链氨基转移酶（hBCATm）反应中间体的晶体结构为hBCATm的动力学确定的底物特异性提供了结构解释。酮亚胺中间体中的异亮氨酸侧链占据可由三个表面限定的疏水结合口袋。酮亚胺结构上氨基酸的建模表明，非底物氨基酸（如芳香族氨基酸、丙氨酸或天冬氨酸）的侧链不能通过货车德瓦尔斯相互作用相互作用或具有空间冲突。还阐明了哺乳动物BCAT对还原剂敏感性的结构和生化基础。hBCATm中的两个半胱氨酸残基Cys315和Cys318（CXXC）是可调节hBCATm活性的氧化还原控制机制的一部分。Cys315和Cys318周围的残基在原核和真核BCAT序列中显示出相当大的序列保守性，然而，CXXC基序仅在哺乳动物蛋白中发现。结果表明，BCAT酶可能会加入列表中的酶，可以通过氧化还原状态进行调节。(C)2003 Elsevier Science B.V.保留所有权利。
Crystal structures of the fold type IV pyridoxal phosphate (PLP)-dependent human mitochondrial branched chain aminotransferase (hBCATm) reaction intermediates have provided a structural explanation for the kinetically determined substrate specificity of hBCATm. The isoleucine side chain in the ketimine intermediate occupies a hydrophobic binding pocket that can be defined by three surfaces. Modeling of amino acids on the ketimine structure shows that the side chains of nonsubstrate amino acids such as the aromatic amino acids, alanine, or aspartate either are unable to interact through van der Waals' interactions or have steric clashes. The structural and biochemical basis for the sensitivity of the mammalian BCAT to reducing agents has also been elucidated. Two cysteine residues in hBCATm, Cys315 and Cys318 (CXXC), are part of a redox-controlled mechanism that can regulate hBCATm activity. The residues surrounding Cys315 and Cys318 show considerable sequence conservation in the prokaryotic and eukaryotic BCAT sequences, however, the CXXC motif is found only in the mammalian proteins. The results suggest that the BCAT enzymes may join the list of enzymes that can be regulated by redox status. (C) 2003 Elsevier Science B.V. All rights reserved.