Coenzyme specificity in aldehyde dehydrogenase

influences on coenzyme preference are explored. Lysine 137 (192 in class 1/ 2 ALDH) lies close to the adenine ribose, directly interacting with the ade nine ribose in NAD-specific ALDHs and the 2'-phosphate of NADP in NADP-spec ific ALDHs. Lys-137 in class 3 ALDH interacts with the adenine ribose indir ectly through an intervening water molecule. However, this residue is prese nt in all ALDHs and, as a result, is unlikely to directly influence coenzym e specificity. Glutamate 140 (195) coordinates the 2'- and 3'-hydroxyls of the adenine ribose of NAD in the class 3 tertiary structure. Thus, it appea red that this residue would influence coenzyme specificity. Mutation to asp artate, asparagine, glutamine or threonine shifts the coenzyme specificity towards NADP, but did not completely change the specificity. Still, the mut ants show the 2'-phosphate of NADP is repelled by Glu-140 (195). Although G lu-140 (195) has a major influence on coenzyme specificity, it is not the o nly influence since class 3 ALDHs, can use both coenzymes, and class 2 ALDH s, which are NAD-specific, have a glutamate at this position. One explanati on may be that the larger space between Lys-137 (192) and the adenine ribos e hydroxyls in the class 3 ALDH:NAD binary structure may provide space to a ccommodate the 2'-phosphate of NADP. Also, a structural shift upon binding NADP may also occur in class 3 ALDHs to help accommodate the 2'-phosphate o f NADP. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.