Differences in nucleotide specificity and catalytic mechanism between Vibrio harveyi aldehyde dehydrogenase and other members of the aldehyde dehydrogenase superfamily

The fatty aldehyde dehydrogenase (Vh-ALDH) isolated from the luminescent bacterium, Vibrio harveyi, differs from other aldehyde dehydrogenases in its high affinity for NADP(+). The binding of NADP(+) appears to arise from the interaction of the 2'-phosphate of the adenosine moiety of NADP(+) with a threonine (T175) in the nucleotide recognition site just after the beta(B) strand as well as with an arginine (R210) that pi stacks over the adenosine moiety. The active site of Vh-ALDH contains the usual suspects of a cysteine (C289), two glutamates (E253 and E377) and an asparagine (N147) involved in the aldehyde dehydrogenase mechanism. However, Vh-ALDH has one polar residue in the active site that distinguishes it from other ALDHs; a histidine (H450) is in close contact with the cysteine nucleophile. As a glutamate has been implicated in promoting the nucleophilicity of the active site cysteine residue in ALDHs, the close contact of a histidine with the cysteine nucleophile in Vh-ALDH raises the possibility of alternate routes to increase the reactivity of the cysteine nucleophile. The effects of mutation of these residues on the different functions catalyzed by Vh-ALDH including acylation, (thio)esterase, reductase and dehydrogenase activities should help define the specific roles of the residues in the active site of ALDHs.