ternary complex of isoform R67 with dihydrofolate and NADPH, resolved to 1.26 A. In the catalytic complex, the polar backbone atoms of two symmetry-related I68 residues provide recognition motifs that interact with the carboxamide on the nicotinamide ring, and the N3-O4 amide function on the pteridine ring. This set of interactions orients the aromatic rings of substrate and cofactor in a relative endo geometry in which the reactive centers are held in close proximity. Additionally, a central, hydrogen-bonded network consisting of two pairs of Y69-Q67/Q67-Y69 residues provides a tight interface, which holds the substrates in place in an orientation conductive to hydride transfer |
Escherichia coli |