Enzymatic Characterization of the Isocitrate Dehydrogenase with Dual Coenzyme Specificity from the Marine Bacterium Umbonibacter marinipuiceus

Isocitrate dehydrogenase (IDH) can be divided into NAD(+)-dependent and NADP(+)-dependent types based on the coenzyme specificity. It is worth noting that some IDHs exhibit dual coenzyme specificity characteristics. Herein, a dual coenzyme-dependent IDH from Umbonibacter Marinipuiceus (UmIDH) was expressed, purified, and identified in detail for the first time. SDS-PAGE and Gel filtration chromatography analyses showed that UmIDH is an 84.7 kDa homodimer in solution. The K(m) values for NAD(+) and NADP(+) are 1800.0 ± 64.4 μM and 1167.7 ± 113.0 μM in the presence of Mn(2+), respectively. Meanwhile, the catalytic efficiency (k(cat)/K(m)) of UmIDH is only 2.3-fold greater for NADP(+) than NAD(+). The maximal activity for UmIDH occurred at pH 8.5 (with Mn(2+)) or pH 8.7 (with Mg(2+)) and at 35 °C (with Mn(2+) or Mg(2+)). Heat inactivation assay revealed that UmIDH sustained 50% of maximal activity after incubation at 57 °C for 20 min with either Mn(2+) or Mg(2+). Moreover, three putative core coenzyme binding residues (R345, L346, and V352) of UmIDH were evaluated by site-directed mutagenesis. This recent work identified a unique dual coenzyme-dependent IDH and achieved the groundbreaking bidirectional modification of this specific IDH’s coenzyme dependence for the first time. This provides not only a reference for the study of dual coenzyme-dependent IDH, but also a basis for the investigation of the coenzyme-specific evolutionary mechanisms of IDH.