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Malate dehydrogenase is a multimeric enzyme among living organisms that catalyzes the reverse transformation of malate and oxaloacetate using the reduction of NAD+ to NADH. This reaction plays a role in metabolic pathways including the citric acid cycle, gluconeogenesis, and anaerobic metabolism. MDH shares a similar 3-dimensional structure and mechanism with lactate dehydrogenase. Knowing the structure is important when it comes to the redesign of enzyme mutations, which can be a useful method for studying the catalysis of small substrates. Physiological effects of the amino acid sequence alterations are easier to predict when the structure is known. The active site of MDH consists of a hydrophobic vacuole containing binding site for the substrate and nicotinamide ring of the coenzyme. Within the active site there is a loop region containing amino acids 119-137. The active site exhibits an open conformation when the substrate or cofactor is bound and a closed conformation when nothing is bound. The charges within the loop region position the substrate in the correct orientation for efficient catalysis.
It was shown that Lysine125, within the loop region of MDH, made essential interactions with co-factor and nearby residues that may have been involved in catalysis (Shania, 2019). Shown in figure 1, Lys125 and R124 are in close proximity with each other. Since both molecules have a positive charge, they are repelling against each other. We are predicting that the position of Lys125 and R124 are causing G263 to have a less stable hydrogen bond. We hypothesized that if Alanine replaces Lysine at position 125, then Arg124 will have a better position and be more stably bound to G263 resulting in a better guide for the substrate to the active site.
Mutagenesis; Lysine; Malate dehydrogenase
Prieve, Taylor and Wallmow, Cathryn, "Site-Directed Mutagenesis of Lysine 125 in Malate Dehydrogenase" (2023). Undergraduate Research Symposium 2023. 4.