Recombinant Klebsiella pneumoniae subsp. pneumoniae NAD-dependent malic enzyme (maeA), partial
Description
Enzymatic Function and Biochemical Properties
The malic enzyme (EC 1.1.1.38) is a key component of bacterial metabolism, facilitating the conversion of malate to pyruvate while generating NADH. In K. pneumoniae, the maeA gene encodes an NAD-dependent isoform distinct from the NADP-dependent malic enzyme (MaeB).
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Catalytic Activity:
Studies on homologous enzymes in Escherichia coli reveal that MaeA exhibits dual functionality, acting as both a malic enzyme and a fumarase . When provided with fumarate as a substrate, E. coli MaeA catalyzes its conversion to malate (K₀.₅ = 13 mM) and subsequently to pyruvate . -
Structural Insights:
The enzyme’s structure includes conserved residues critical for cofactor specificity. In Thermococcus kodakarensis, directed evolution studies identified key residues (e.g., Arg297, Glu303) that determine NAD⁺/NADP⁺ preference . Similar residues likely govern cofactor specificity in K. pneumoniae maeA.
Research Findings and Comparisons
Table 1 summarizes key findings from studies on maeA and related enzymes:
Implications for Pathogenesis and Biotechnology
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Pathogenesis: maeA’s role in pyruvate metabolism may enhance K. pneumoniae’s ability to survive in host environments, such as during bloodstream infections .
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Biotechnological Applications: Engineering maeA in K. pneumoniae could optimize malate or pyruvate production for industrial bioprocesses, leveraging its dual enzymatic activity .
