The 1.9 A structure of the branched-chain amino-acid transaminase (IlvE) from Mycobacterium tuberculosis.
The 1.9 A structure of the branched-chain amino-acid transaminase (IlvE) from Mycobacterium tuberculosis.
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DOI：
10.1107/s1744309109036690
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发表时间：
2009-11
期刊：
影响因子：
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通讯作者：
L. Tremblay;J. Blanchard
中科院分区：
文献类型：
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作者：
L. Tremblay;J. Blanchard
与哺乳动物不同，细菌编码合成支链氨基酸的酶。依赖于50-磷酸的吡哆醛转氨酶在这些途径中执行最终的生物合成步骤，将酮酸前体转化为-氨基酸。结核分枝杆菌支链氨基酸转氨酶(MtIlvE)已被结晶，其结构已在1.9埃分辨率下解析。MtIlvE单体由两个相互作用形成活性部位的结构域组成。ILVE的生物活性形式是一种同源二聚体，其中每个单体都为伴侣分子贡献了一个底物专一性环。额外的底物选择性可以由保守的N-末端Phe30残基提供，以前已经观察到它保护了IV型折叠同源二聚体中的活性部位。MtIlvE的活性中心含有与结合的PMP对应的密度，这很可能是结晶介质中存在胰蛋白内酯的结果。此外，两个半胱氨酸残基位于二聚体界面，在氧化条件下形成二硫键。目前尚不清楚它们是否参与了任何类似于人类线粒体支链氨基酸转氨酶的调节活动。
Unlike mammals, bacteria encode enzymes that synthesize branched-chain amino acids. The pyridoxal 50-phosphate-dependent transaminase performs the final biosynthetic step in these pathways, converting keto acid precursors into -amino acids. The branched-chain amino-acid transaminase from Mycobacterium tuberculosis (MtIlvE) has been crystallized and its structure has been solved at 1.9 angstrom resolution. The MtIlvE monomer is composed of two domains that interact to form the active site. The biologically active form of IlvE is a homodimer in which each monomer contributes a substrate-specificity loop to the partner molecule. Additional substrate selectivity may be imparted by a conserved N-terminal Phe30 residue, which has previously been observed to shield the active site in the type IV fold homodimer. The active site of MtIlvE contains density corresponding to bound PMP, which is likely to be a consequence of the presence of tryptone in the crystallization medium. Additionally, two cysteine residues are positioned at the dimer interface for disulfide-bond formation under oxidative conditions. It is unknown whether they are involved in any regulatory activities analogous to those of the human mitochondrial branched-chain amino-acid transaminase.