Efforts Toward the Direct Experimental Characterization of Enzyme Microenvironments: TyrosinelOO in Dihydrofolate Reductase

摘要

The enzyme dihydrofolate reductase (DHFR), which catalyzes hydride transfer from the cofactor nicotinamide adenine dinucleotide phosphate (NADPH) to 7,8-dihydrofolate to produce tetrahydrofolate, has emerged as a paradigm for the study of enzyme catalysis.'1"31 It has been suggested that electrostatic complementarity between the enzyme and the transition state for hydride transfer contributes significantly to catalysis, and computational studies have identified a number of residues that may mediate these interactions. One of the most important is Tyr100, which directly contacts the nicotinamide hydride donor (Figure 1) and is thought to stabilize the developing positive charge on the cofactor in the hydride-transfer transition state. However, protein dynamics have also been suggested to contribute to DHFR catalysis through the population of rare but reactive substrate conformations.