Single amino acid exchanges affect the substrate preference of an acetaldehyde dehydrogenase.

The NAD-dependent aldehyde dehydrogenase AldB from Aromatoleum aromaticum was recombinantly produced in Escherichia coli and biochemically characterized. As suggested by its substrate spectrum, the most probably physiological function of AldB is the oxidation of short aliphatic aldehydes such as acetaldehyde, which occur as intermediates in the degradation of the corresponding alcohols. In addition, we generated some mutant variants in residue Tyr460, which is located at the neck region of the substrate channel and analyzed their effects on the catalytic parameters for different substrates. Single amino acid exchanges at this position revealed profound changes in substrate preference and substrate inhibition of the variants. KEY POINTS: • Small aliphatic aldehydes show the best catalytic efficiency with aldehyde dehydrogenase AldB • Amino acid exchanges at Y460 results in changed catalytic efficiencies and substrate inhibition • AldB is a member of a new clade of the aldehyde dehydrogenase superfamily.