Nasir Nazia, Anant Avishek, Vyas Rajan, Biswal Bichitra Kumar
Protein Crystallography Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, Delhi, 110067, India.
Sci Rep. 2016 Jan 7;6:18880. doi: 10.1038/srep18880.
Aminotransferases of subfamily Iβ, which include histidinol phosphate aminotransferases (HspATs) and aromatic amino acid aminotransferases (ArATs), are structurally similar but possess distinct substrate specificities. This study, encompassing structural and biochemical characterisation of HspAT and ArAT from Mycobacterium tuberculosis demonstrates that the residues lining the substrate binding pocket and N-terminal lid are the primary determinants of their substrate specificities. In mHspAT, hydrophilic residues in the substrate binding pocket and N-terminal lid allow the entry and binding of its preferential substrate, Hsp. On the other hand, the hydrophobic nature of both the substrate binding pocket and the N-terminal lid of mArAT is responsible for the discrimination of a polar substrate such as Hsp, while facilitating the binding of Phe and other aromatic residues such as Tyr and Trp. In addition, the present study delineates the ligand induced conformational rearrangements, providing insights into the plasticity of aminotransferases. Furthermore, the study also demonstrates that the adventitiously bound ligand 2-(N-morpholino)ethanesulfonic acid (MES) is indeed a specific inhibitor of HspAT. These results suggest that previously untapped morpholine-ring scaffold compounds could be explored for the design of new anti-TB agents.
Iβ亚家族的氨基转移酶，包括组氨醇磷酸氨基转移酶（HspATs）和芳香族氨基酸氨基转移酶（ArATs），结构相似但具有不同的底物特异性。这项涵盖结核分枝杆菌HspAT和ArAT的结构与生化特性的研究表明，底物结合口袋和N端盖子内部的残基是其底物特异性的主要决定因素。在结核分枝杆菌HspAT（mHspAT）中，底物结合口袋和N端盖子中的亲水性残基允许其优先底物Hsp进入并结合。另一方面，结核分枝杆菌ArAT（mArAT）的底物结合口袋和N端盖子的疏水性导致对极性底物如Hsp的排斥，同时促进苯丙氨酸以及其他芳香族残基如酪氨酸和色氨酸的结合。此外，本研究描绘了配体诱导的构象重排，为氨基转移酶的可塑性提供了见解。此外，该研究还表明，偶然结合的配体2-（N-吗啉代）乙磺酸（MES）确实是HspAT的特异性抑制剂。这些结果表明，可以探索以前未开发的吗啉环支架化合物来设计新型抗结核药物。
