Lima Santiago, Sundararaju Bakthavatsalam, Huang Christina, Khristoforov Roman, Momany Cory, Phillips Robert S
Department of Biochemistry and Molecular Biology, The University of Georgia, Athens, GA 30602, USA.
J Mol Biol. 2009 Apr 24;388(1):98-108. doi: 10.1016/j.jmb.2009.02.055. Epub 2009 Mar 2.
The Pseudomonas dacunhael-aspartate-beta-decarboxylase (ABDC, aspartate 4-decarboxylase, aspartate 4-carboxylyase, E.C. 4.1.1.12) is a pyridoxal-5'-phosphate (PLP)-dependent enzyme that catalyzes the beta-decarboxylation of l-aspartate to produce l-alanine and CO(2). This catalytically versatile enzyme is known to form functional dodecamers at its optimal pH and is thought to work in conjunction with an l-Asp/l-Ala antiporter to establish a proton gradient across the membrane that can be used for ATP biosynthesis. We have solved the atomic structure of ABDC to 2.35 A resolution using single-wavelength anomalous dispersion phasing. The structure reveals that ABDC oligomerizes as a homododecamer in an unknown mode among PLP-dependent enzymes and has highest structural homology with members of the PLP-dependent aspartate aminotransferase subfamily. The structure shows that the ABDC active site is very similar to that of aspartate aminotransferase. However, an additional arginine side chain (Arg37) was observed flanking the re-side of the PLP ring in the ABDC active site. The mutagenesis results show that although Arg37 is not required for activity, it appears to be involved in the ABDC catalytic cycle.
假单胞菌天冬氨酸-β-脱羧酶（ABDC，天冬氨酸4-脱羧酶，天冬氨酸4-羧基裂解酶，E.C. 4.1.1.12）是一种依赖磷酸吡哆醛（PLP）的酶，催化L-天冬氨酸的β-脱羧反应生成L-丙氨酸和CO₂。已知这种具有多种催化功能的酶在其最适pH值下形成功能性十二聚体，并且被认为与L-天冬氨酸/L-丙氨酸反向转运体协同作用，以建立跨膜质子梯度，该质子梯度可用于ATP生物合成。我们使用单波长反常色散相位法将ABDC的原子结构解析到了2.35 Å的分辨率。该结构表明，ABDC在依赖PLP的酶中以一种未知模式寡聚为同型十二聚体，并且与依赖PLP的天冬氨酸转氨酶亚家族成员具有最高的结构同源性。结构显示ABDC的活性位点与天冬氨酸转氨酶的活性位点非常相似。然而，在ABDC活性位点中，观察到PLP环的Re侧有一个额外的精氨酸侧链（Arg37）。诱变结果表明，虽然Arg37对于活性不是必需的，但它似乎参与了ABDC的催化循环。
