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NMR structure and dynamics of the NADH nicotinamide ring bound to dihydrodipicolinate reductase

The current development of NMR methods facilitates the study of the mechanism by which enzymes catalyze reactions. The focus of this study is the dynamics and geometry of cofactor NAD(H) upon its binding to a dehydrogenase. To facilitate NMR analysis, the NAD(H) carboxamide was labeled with 15N (15N‐CA). CPMG relaxation dispersion measurements for free [15N‐CA]‐NAD+ showed millisecond timescale conformation exchange, consistent with previous report of exchange between open/closed conformations. Interestingly, in the complex of E. coli dihydrodipicolinate reductase (DHPR) and [15N‐CA]‐NADH, the relaxation dispersion curve also indicated conformational exchange; upon addition of the DHPR substrate analog pyridine 2,6‐dicarboxylate, the exchanged is no longer observed, indicating restricted motion induced by substrate binding.