Fan C, Moews P C, Walsh C T, Knox J R
Department of Molecular and Cell Biology, University of Connecticut, Storrs 06269-3125.
Science. 1994 Oct 21;266(5184):439-43. doi: 10.1126/science.7939684.
The molecular structure of the D-alanine:D-alanine ligase of the ddlB gene of Escherichia coli, co-crystallized with an S,R-methylphosphinate and adenosine triphosphate, was determined by x-ray diffraction to a resolution of 2.3 angstroms. A catalytic mechanism for the ligation of two D-alanine substrates is proposed in which a helix dipole and a hydrogen-bonded triad of tyrosine, serine, and glutamic acid assist binding and deprotonation steps. From sequence comparison, it is proposed that a different triad exists in a recently discovered D-alanine:D-lactate ligase (VanA) present in vancomycin-resistant enterococci. A molecular mechanism for the altered specificity of VanA is suggested.
通过X射线衍射确定了与S，R-甲基次膦酸酯和三磷酸腺苷共结晶的大肠杆菌ddlB基因的D-丙氨酸：D-丙氨酸连接酶的分子结构，分辨率为2.3埃。提出了一种用于连接两个D-丙氨酸底物的催化机制，其中螺旋偶极子以及酪氨酸、丝氨酸和谷氨酸的氢键三联体协助结合和去质子化步骤。通过序列比较，提出在耐万古霉素肠球菌中最近发现的D-丙氨酸：D-乳酸连接酶（VanA）中存在不同的三联体。提出了VanA特异性改变的分子机制。
