Crystal structure of the NADP(+)-dependent aldehyde dehydrogenase from Vibrio harveyi: structural implications for cofactor specificity and affinity

Aldehyde dehydrogenase from the bioluminescent bacterium, Vibrio harveyi, c atalyses the oxidation of long-chain aliphatic aldehydes to acids. The enzy me is unique compared with other forms of aldehyde dehydrogenase in that it exhibits a very high specificity and affinity for the cofactor NADP(+). St ructural studies of this enzyme and comparisons with other forms of aldehyd e dehydrogenase provide the basis for understanding the molecular features that dictate these unique properties and will enhance our understanding of the mechanism of catalysis for this class of enzyme. The X-ray structure of aldehyde dehydrogenase from V. harveyi has been solved to 2.5-Angstrom res olution as a partial complex with the cofactor NADP(+) and to 2.1-Angstrom resolution as a fully bound 'holo' complex. The cofactor preference exhibit ed by different forms of the enzyme is predominantly determined by the elec trostatic environment surrounding the 2'-hydroxy or the 2'-phosphate groups of the adenosine ribose moiety of NAD(+) or NADP(+), respectively. In the NADP(+)-dependent structures the presence of a threonine and a lysine contr ibute to the cofactor specificity. In the V. harveyi enzyme an arginine res idue (Arg 210) contributes to the high cofactor affinity through a pi stack ing interaction with the adenine ring system of the cofactor. Further diffe rences between the V. harveyi enzyme and other aldehyde dehydrogenases are seen in the active site, in particular histidine residue which is structura lly conserved with phosphorylating glyceraldehyde-3-phosphate dehydrogenase . This may suggest an alternative mechanism for activation of the reactive cysteine residue for nucleophilic attack.