Vyas Rajan, Tewari Rupinder, Weiss Manfred S, Karthikeyan Subramanian
Department of Biotechnology, Panjab University, Chandigarh 160 014, India.
Acta Crystallogr D Biol Crystallogr. 2012 Jun;68(Pt 6):671-9. doi: 10.1107/S0907444912007330. Epub 2012 May 17.
Aspartate-semialdehyde dehydrogenase (Asd; ASADH; EC 1.2.1.11) is the enzyme that lies at the first branch point in the biosynthetic pathway of important amino acids including lysine and methionine and the cell-wall component diaminopimelate (DAP). The enzymatic reaction of ASADH is the reductive dephosphorylation of aspartyl-β-phosphate (ABP) to aspartate β-semialdehyde (ASA). Since the aspartate pathway is absolutely essential for the survival of many microbes and is absent in humans, the enzymes involved in this pathway can be considered to be potential antibacterial drug targets. In this work, the structure of ASADH from Mycobacterium tuberculosis H37Rv (Mtb-ASADH) has been determined in complex with glycerol and sulfate at 2.18 Å resolution and in complex with S-methyl-L-cysteine sulfoxide (SMCS) and sulfate at 1.95 Å resolution. The overall structure of Mtb-ASADH is similar to those of its orthologues. However, in the Mtb-ASADH-glycerol complex structure the glycerol molecule is noncovalently bound to the active-site residue Cys130, while in the Mtb-ASADH-SMCS complex structure the SMCS (Cys) is covalently linked to Cys130. The Mtb-ASADH-SMCS complex structurally mimics one of the intermediate steps in the proposed mechanism of ASADH enzyme catalysis. Comparison of the two complex structures revealed that the amino acids Glu224 and Arg249 undergo conformational changes upon binding of glycerol. Moreover, the structures reported here may help in the development of species-specific antibacterial drug molecules against human pathogens.
天冬氨酸半醛脱氢酶（Asd；ASADH；EC 1.2.1.11）是一种酶，它处于包括赖氨酸、蛋氨酸以及细胞壁成分二氨基庚二酸（DAP）在内的重要氨基酸生物合成途径的第一个分支点。ASADH的酶促反应是将天冬氨酰-β-磷酸（ABP）还原脱磷酸化为天冬氨酸β-半醛（ASA）。由于天冬氨酸途径对许多微生物的生存绝对至关重要，而在人类中不存在，因此参与该途径的酶可被视为潜在的抗菌药物靶点。在这项工作中，已确定结核分枝杆菌H37Rv（Mtb-ASADH）的天冬氨酸半醛脱氢酶与甘油和硫酸盐形成复合物的结构，分辨率为2.18 Å，以及与S-甲基-L-半胱氨酸亚砜（SMCS）和硫酸盐形成复合物的结构，分辨率为1.95 Å。Mtb-ASADH的整体结构与其同源物相似。然而，在Mtb-ASADH-甘油复合物结构中，甘油分子非共价结合到活性位点残基Cys130上，而在Mtb-ASADH-SMCS复合物结构中，SMCS（Cys）与Cys130共价连接。Mtb-ASADH-SMCS复合物在结构上模拟了ASADH酶催化作用机制中提出的中间步骤之一。两种复合物结构的比较表明，氨基酸Glu224和Arg249在结合甘油后会发生构象变化。此外，这里报道的结构可能有助于开发针对人类病原体的物种特异性抗菌药物分子。
