The goal of the research program described in this application is to obtain a deeper understanding of how rapid protein dynamics, so called promoting vibrations on a sub picosecond timescale, are employed and incorporated into both natural and artificially designed enzymes. Over the years we have identified such motions in a variety of enzymatically catalyzed reactions, and also found them missing in at least one. Our goal for the long term is to decipher how nature has used this approach as an engineering principle and how it has been incorporated as a part of the function. For example, many studies have now found that in hydride transfer enzymes such as alcohol dehydrogenase, rapid motion of the donor to the acceptor facilitates the chemical step by lowering the effective adiabatic barrier. We also study two seemingly dichotomous views of enzyme function ? the electrostatic view, and the dynamic view. It is entirely possible that the electric field milieu both contributes strongly to catalysis, and in certain cases is modulated by the same types of motions that for example control donor acceptor distance. Because our methods allow us to harvest ensembles of reactive trajectories, exactly such mechanisms can be studied. Finally, there exist cases in which naturally occurring enzymes exhibit simple and direct chemistry, while single mutations cause significant complexities in kinetic analysis. It is simply not clear how this can come about. In order to pursue this research we propose to implement the following three specific aims:
Aim 1 : We will study one of the more successful attempts in synthetic enzymatic chemistry ? the artificial creation of retro-aldolases. We will ascertain whether theoretical design coupled to laboratory evolution of these artificial protein catalysts caused change in the coupling of protein dynamics to reaction.
Aim 2 : We will study how electric field varies in the active site of an enzyme as the reaction proceeds from reactants to products through a transition state. Catechol-O-methyltransferase (COMT) is an enzyme in which both protein dynamics and electrostatic preorganization have been stated emphatically by other groups to produce the catalytic effect. In particular we will identify if there is a promoting vibration as part of the reaction coordinate in this enzyme, and how it may help to control the field environment.
Aim 3 : We will analyze reactions catalyzed by the poorly understood ?ene-reductase? family. We will address the importance of protein dynamics and the ability of a single point mutation to create multiple reaction ?configurations? with highly divergent kinetic behavior. After decades of study, the deceptively simple question of how enzymes work is still a hotbed of debate. Via such studies as here proposed we contribute to both basic knowledge and eventual practical control application.
A deeper understanding of the contribution of rapid protein dynamics to enzymatic chemistry, and how nature and laboratory evolution has molded dynamics in the protein will lead to a deeper understanding of enzymatic mechanism, new modes of inhibition, and the tailoring of proteins for biomedical use.