Efficient Binding of Flexible and Redox-Active Coenzymes by Oxidoreductases

Abstract

Although how an enzyme binds its substrate and rate-limiting transition state is well-studied, how it binds a flexible redox-active coenzyme, which may adopt different native solution conformations when oxidized/reduced, remains unclear. Using the coenzyme nicotinamide adenine dinucleotide (NAD) as an example, we show that redox enzymes bind oxidized NAD+ and reduced NADH in similar conformations that are between folded NAD+ and extended NADH solution conformations. By preorganizing the coenzyme-binding site to bind such an “intermediate” conformation, a redox enzyme can efficiently bind oxidized and reduced NAD, whereas having to substantially reorganize the binding site to accommodate the NAD product might impede catalysis.