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Improving the NADH-cofactor specificity of the highly active AdhZ3 and AdhZ2 from Escherichia coli K-12

Pick, André, Ott, Wolfgang, Howe, Thomas, Schmid, Jochen, Sieber, Volker
Journal of biotechnology 2014 v.189 pp. 157-165
Escherichia coli K12, NAD (coenzyme), NADP (coenzyme), alcohol dehydrogenase, alcohols, asparagine, biocatalysis, biomass, enzymatic reactions, horses, liver, mutagenesis, nicotinamide, screening
Biocatalysis is a promising tool for the sustainable production of chemicals. When cofactor depending enzymatic reactions are involved the applicability of the right cofactor is a central issue. One important example in this regard is the production of alcohols by nicotinamide cofactor (NAD(P)+) depending alcohol dehydrogenases. AdhZ3 from Escherichia coli, which is important for the production of alcohols from biomass, has a preference for NADPH as cofactor. We used a structure guided site-specific random approach, to change the cofactor preference towards NADH and to deduce more general rules for redesigning the cofactor specificity. Transfer of a triplet motif from NADH preferring horse liver ADH to AdhZ3 showed an insufficient switch in the preference towards NADH. A combinatorial site saturation mutagenesis altering three residues at once was applied. Library screening with two different cofactor concentrations (0.1 and 0.3mM) resulted in nine improved variants with AdhZ3-LND having the highest vmax and AdhZ3-CND having the lowest Km. Asparagine was the most frequent amino acid found in eight of nine triplet motifs. To verify the triplet-motif, two variants of E. coli AdhZ2 DIN and LND were designed and confirmed for improved activity with NADH.