Pradhan Anupam, Mukherjee Prasenjit, Tripathi Abhai K, Avery Mitchell A, Walker Larry A, Tekwani Babu L
National Center for Natural Products Research, School of Pharmacy, University of Mississippi, University, MS 38677, USA.
Mol Cell Biochem. 2009 May;325(1-2):141-8. doi: 10.1007/s11010-009-0028-2. Epub 2009 Jan 29.
L-Malate dehydrogenase (PfMDH) from Plasmodium falciparum, the causative agent for the most severe form of malaria, has shown remarkable similarities to L: -lactate dehydrogenase (PfLDH). PfMDH is more closely related to [LDH-like] MDHs characterized in archae and other prokaryotes. Initial sequence analysis and identification of critical amino acid residues involved in inter-subunit salt-bridge interactions predict tetrameric structure for PfMDH. The catalytically active recombinant PfMDH was characterized as a tetramer. The enzyme is localized primarily in the parasites cytosol. To gain molecular insights into PfMDH/PfLDH relationships and to understand the quaternary structure of PfMDH, dimers were generated by mutation to the potential salt-bridge interacting sites. The R183A and R214G mutations, which snapped the salt bridges between the dimers and resulted in lower dimeric state, did not affect catalytic properties of the enzyme. The mutant dimers of PfMDH were active equally as the wild-type PfMDH. The studies reveal structure of PfMDH as a dimer of dimers. The tetrameric state of PfMDH was not essential for catalytic functions of the enzyme but may be an evolutionary adaptation for cytosolic localization to support its role in NAD/NADH coupling, an important metabolic function for survival of the malaria parasite.
恶性疟原虫（导致最严重疟疾形式的病原体）的L-苹果酸脱氢酶（PfMDH）与L-乳酸脱氢酶（PfLDH）表现出显著的相似性。PfMDH与古细菌和其他原核生物中所描述的[类似LDH的]MDH关系更为密切。对参与亚基间盐桥相互作用的关键氨基酸残基进行的初步序列分析和鉴定预测PfMDH为四聚体结构。具有催化活性的重组PfMDH被鉴定为四聚体。该酶主要定位于寄生虫的细胞质中。为了深入了解PfMDH/PfLDH之间的关系并理解PfMDH的四级结构，通过对潜在的盐桥相互作用位点进行突变生成了二聚体。R183A和R214G突变破坏了二聚体之间的盐桥并导致较低的二聚体状态，但并未影响该酶的催化特性。PfMDH的突变二聚体与野生型PfMDH具有同等活性。这些研究揭示PfMDH的结构为二聚体的二聚体。PfMDH的四聚体状态对于该酶的催化功能并非必需，但可能是一种进化适应性，用于细胞质定位，以支持其在NAD/NADH偶联中的作用，这是疟原虫生存的一项重要代谢功能。
