Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan, 48109.
Protein Sci. 2013 Oct;22(10):1417-24. doi: 10.1002/pro.2315. Epub 2013 Aug 28.
α-Aminoadipate aminotransferase (AAA-AT) catalyzes the amination of 2-oxoadipate to α-aminoadipate in the fourth step of the α-aminoadipate pathway of lysine biosynthesis in fungi. The aromatic aminotransferase Aro8 has recently been identified as an AAA-AT in Saccharomyces cerevisiae. This enzyme displays broad substrate selectivity, utilizing several amino acids and 2-oxo acids as substrates. Here we report the 1.91Å resolution crystal structure of Aro8 and compare it to AAA-AT LysN from Thermus thermophilus and human kynurenine aminotransferase II. Inspection of the active site of Aro8 reveals asymmetric cofactor binding with lysine-pyridoxal-5-phosphate bound within the active site of one subunit in the Aro8 homodimer and pyridoxamine phosphate and a HEPES molecule bound to the other subunit. The HEPES buffer molecule binds within the substrate-binding site of Aro8, yielding insights into the mechanism by which it recognizes multiple substrates and how this recognition differs from other AAA-AT/kynurenine aminotransferases.
α-氨基己二酸氨基转移酶（AAA-AT）在真菌赖氨酸生物合成的α-氨基己二酸途径的第四步中催化 2-氧代己二酸与α-氨基己二酸的胺化。最近，芳香族氨基转移酶 Aro8 被鉴定为酿酒酵母中的一种 AAA-AT。该酶显示出广泛的底物选择性，可利用几种氨基酸和 2-氧代酸作为底物。在此，我们报告了 Aro8 的 1.91Å 分辨率晶体结构，并将其与来自嗜热脂肪芽孢杆菌的 LysN 和人犬尿氨酸氨基转移酶 II 的 AAA-AT 进行了比较。对 Aro8 的活性位点进行检查，发现不对称辅因子结合，赖氨酸-吡哆醛-5-磷酸结合在 Aro8 同源二聚体的一个亚基的活性位点内，而吡哆胺磷酸和 HEPES 分子结合在另一个亚基上。HEPES 缓冲分子结合在 Aro8 的底物结合位点内，深入了解了它识别多种底物的机制，以及这种识别与其他 AAA-AT/犬尿氨酸氨基转移酶的不同之处。
