Jang Eun Hyuk, Park Seong Ah, Chi Young Min, Lee Ki Seog
Department of Biosystems and Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul 136-713, Korea.
Department of Clinical Laboratory Science, College of Health Sciences, Catholic University of Pusan, Busan 609-757, Korea.
Mol Cells. 2014 Oct 31;37(10):719-26. doi: 10.14348/molcells.2014.0162. Epub 2014 Sep 26.
The γ-Aminobutyric acid (GABA) that is found in prokaryotic and eukaryotic organisms has been used in various ways as a signaling molecule or a significant component generating metabolic energy under conditions of nutrient limitation or stress, through GABA catabolism. Succinic semialdehyde dehydrogenase (SSADH) catalyzes the oxidation of succinic semialdehyde to succinic acid in the final step of GABA catabolism. Here, we report the catalytic properties and two crystal structures of SSADH from Streptococcus pyogenes (SpSSADH) regarding its cofactor preference. Kinetic analysis showed that SpSSADH prefers NADP(+) over NAD(+) as a hydride acceptor. Moreover, the structures of SpSSADH were determined in an apo-form and in a binary complex with NADP(+) at 1.6 Å and 2.1 Å resolutions, respectively. Both structures of SpSSADH showed dimeric conformation, containing a single cysteine residue in the catalytic loop of each subunit. Further structural analysis and sequence comparison of SpSSADH with other SSADHs revealed that Ser158 and Tyr188 in SpSSADH participate in the stabilization of the 2'-phosphate group of adenine-side ribose in NADP(+). Our results provide structural insights into the cofactor preference of SpSSADH as the gram-positive bacterial SSADH.
在原核生物和真核生物中发现的γ-氨基丁酸（GABA），已通过GABA分解代谢，以多种方式用作信号分子或在营养限制或应激条件下产生代谢能量的重要成分。琥珀酸半醛脱氢酶（SSADH）在GABA分解代谢的最后一步催化琥珀酸半醛氧化为琥珀酸。在此，我们报告了化脓性链球菌（SpSSADH）的SSADH关于其辅因子偏好的催化特性和两个晶体结构。动力学分析表明，SpSSADH优先选择NADP（+）而非NAD（+）作为氢化物受体。此外，SpSSADH的结构分别以脱辅基形式和与NADP（+）的二元复合物形式在1.6 Å和2.1 Å分辨率下确定。SpSSADH的两种结构均显示二聚体构象，每个亚基的催化环中含有一个半胱氨酸残基。SpSSADH与其他SSADH的进一步结构分析和序列比较表明，SpSSADH中的Ser158和Tyr188参与了NADP（+）中腺嘌呤侧核糖2'-磷酸基团的稳定。我们的结果为作为革兰氏阳性细菌SSADH的SpSSADH的辅因子偏好提供了结构见解。
