Aldehyde Reductase: The Role of C-Terminal Residues in Defining Substrate and Cofactor Specificities

Aldose and aldehyde reductases: Correlation of molecular modeling and mass spectrometric studies on the binding of inhibitors to the active site

“…27 A major difference observed in the crystal structures of the two enzymes is the participation of an eight-residue insertion segment from the C-terminal loop of ALR1 (residues 306-313) in lining the active site pocket. 24,25 The role of the C-terminal loop in the binding of inhibitor to ALR1 has been investigated by using a site-directed mutagenesis. 16,34 Upon binding of tolrestat and zopolrestat to ALR1, the side chain of the nonconserved Arg 312 (missing in ALR2) moves to accommodate the inhibitor into the active site pocket 16,26 (see Fig.…”

“…22,23 A comparison between the enzyme crystal structures shows that the structure of the active site of ALR1 differs from that of ALR2 due to the participation of an eight-residue insertion segment from the C-terminal loop in lining the active site pocket. 24,25 However, we have recently demonstrated, by using X-ray crystallography and computer modeling, that the inhibitors sorbinil, tolrestat, and zopolrestat are oriented into the active sites of ALR1 and ALR2 in a similar manner. 16 -19,26 The oxygen atoms of the two carbonyl groups of sorbinil form hydrogen bonds with Tyr 50, His 113, and Trp 114 in ALR1 and ALR2 (the sequence numbering for ALR1 is used 27 ).…”

Structure of xylose reductase bound to NAD+ and the basis for single and dual co-substrate specificity in family 2 aldo-keto reductases

“…A porcine aldehyde reductase mutant lacking eight residues in the C-terminal loop has been characterized, which confers an impressive conversion of enzyme specificity from NADPH (wildtype K m = 3.7 µM; mutant K m = 670 µM) into NADH (wild-type K m = 5100 µM; mutant K m = 35 µM) [31]. In the absence of a NAD(H)-bound crystal structure for this enzyme, it is very difficult to reconcile this biochemical data with the changes in the primary structure, because none of the residues make direct contact with the co-substrate in the NADP + -bound holoenzyme structure.…”

Pyrido[1,2-a]pyrimidin-4-one Derivatives as a Novel Class of Selective Aldose Reductase Inhibitors Exhibiting Antioxidant Activity

“…22 The specific opening of the pocket varies to accommodate each inhibitor, producing an "induced fit". Because the residues lining this pocket are not conserved in ALR1, the interactions are specific for ALR2, [47][48][49] and as a result, inhibitors with binding interactions in this "specificity pocket" are generally highly selective for ALR2. 22 The finding that 19 and 29 bind in the above-mentioned hydrophobic pocket accounts for the ALR2 selectivity observed for these inhibitors.…”