Structure-Guided Protein Engineering of Glyceraldehyde-3-phosphate Dehydrogenase from Corynebacterium glutamicum for Dual NAD/NADP Cofactor Specificity

Since the discovery of l-glutamate-producing Corynebacterium glutamicum, it has evolved to be an industrial workhorse. For biobased chemical production, suppling sufficient amounts of the NADPH cofactor is crucial. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a glycolytic enzyme that converts glyceraldehyde-3-phosphate (G3P) to 1,3-bisphosphoglycerate and produces NADH, is a major prospective solution for the cofactor imbalance issue. In this study, we determined the crystal structure of GAPDH from C. glutamicum ATCC13032 (CgGAPDH). Based on the structural information, we generated six CgGAPDH variants, CgGAPDH^L36S, CgGAPDH^L36S/T37K, CgGAPDH^{L36S/T37K/P192S}, CgGAPDH^{L36S/T37K/F100V/P192S}, CgGAPDH^{L36S/T37K/F100L/P192S}, and CgGAPDH^{L36S/T37K/F100I/P192S}, that can produce both NADH and NAPDH. The final CgGAPDH^{L36S/T37K/F100V/P192S} variant showed a 212-fold increase in enzyme activity for NADP as well as 200% and 30% increased activity for the G3P substrate under NAD and NADP cofactor conditions, respectively. In addition, crystal structures of CgGAPDH variants in complex with NAD(P) permit the elucidation of differences between wild-type CgGAPDH and variants in relation to cofactor stabilization.