The global regulation of dynamics and structure mediated by single hydride in a family of reductases

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PROJECT SUMMARY We have discovered that a single hydride induces global changes to both structure and dynamics within multiple members of an enzyme family, providing a fundamental link between enzyme structure, dynamics, and allostery that has implications to the entire oxidoreductase superfamily. Specifically, the BLVRB family are NADPH-dependent reductases present in multiple organisms where they regulate cellular redox through the reduction of biliverdin-to-bilirubin and a wide array of flavin substrates. While our recent publications have revealed that coenzyme binding is coupled to global conformational and dynamic changes, we have now discovered that there are largescale changes coupled to the oxidation state of the coenzyme as far as 23 Å away. Thus, structural catalytic the central premise of this application is that a coenzyme's hydride is globally coupled to both and dynamic changes within an enzyme family and that such global coupling is integrally related to function. The novelty here is that we will explicitly determine how a single hydride, i.e., the difference between NADPH/NADP+, is globally linked (Aim 1) and how this global coupling controls enzyme function (Aim 2). Further innovation includes the following. First, we have discovered that hydride-coupled networks can be modulated by mutations directly to the enzyme/coenzyme interface but also to distally coupled sites, which gives us the unique opportunity to determine the role of these networks in function. Second, we have discovered that evolutionarily changing residues modulate hydride coupled networks and function, providing remarkable insight into the evolutionary role of hydride-mediated coupling and function. Evolutionary differences will therefore be exploited to identify allosteric networks coupled to the oxidative state of the coenzyme and simultaneously reveal their evolutionary roles in function. Based on our preliminary data that includes NMR, X-ray crystallographic, and biochemical studies, we hypothesize that the coenzyme oxidation induces its own conformational change that is further propagated globally through the enzyme in multiple BLVRB family members (referred to as “insideout” coupling) and that networks coupled to these changes modulate function (referred to as “outsidein” coupling). We will address this hypothesis through the following: Aim 1) Determine how a single hydride modulates the global dynamics and structure within the BLVRB family of enzymes. NMR solution studies using CSPs, relaxation studies, and ensembles methods will be used to determine how a single hydride imparts its global regulation to dynamics and structure using three distinct BLVRB family members with both active site and distal differences (human, hyrax, and mosquito). Aim 2) Determine the functional role of networks coupled to the oxidative state of the coenzyme. Biochemical and biophysical methods will be used to determine the functional role of hydride-mediated global regulation, which include both the role of direct interactions with the coenzyme's hydride as well as the role of networks of communication coupled to the coenzyme (allostery).