Malashkevich V N, Onuffer J J, Kirsch J F, Jansonius J N
Department of Structural Biology, University of Basel, Switzerland.
Nat Struct Biol. 1995 Jul;2(7):548-53. doi: 10.1038/nsb0795-548.
Mutation of six residues of Escherichia coli aspartate aminotransferase results in substantial acquisition of the transamination properties of tyrosine amino-transferase without loss of aspartate transaminase activity. X-ray crystallographic analysis of key inhibitor complexes of the hexamutant reveals the structural basis for this substrate selectivity. It appears that tyrosine aminotransferase achieves nearly equal affinities for a wide range of amino acids by an unusual conformational switch. An active-site arginine residue either shifts its position to electrostatically interact with charged substrates or moves aside to allow access of aromatic ligands.
大肠杆菌天冬氨酸转氨酶六个残基的突变导致在不丧失天冬氨酸转氨酶活性的情况下，大量获得酪氨酸转氨酶的转氨特性。对该六突变体关键抑制剂复合物的X射线晶体学分析揭示了这种底物选择性的结构基础。酪氨酸转氨酶似乎通过一种不寻常的构象转换对多种氨基酸实现了几乎相等的亲和力。活性位点的一个精氨酸残基要么移动其位置以与带电荷的底物进行静电相互作用，要么移到一旁以便芳香族配体能够进入。
