Research

Many of the most important questions in enzyme mechanism depend on structural details that can be difficult to establish by diffraction alone: Where are the protons? Which residues are charged? How are hydrogen bonds organized? How does electronic structure change during catalysis?

We develop and apply NMR crystallography — the integration of solid-state NMR, crystallography, and first-principles computational chemistry — to answer these questions at atomic resolution.

A major focus is the characterization of enzyme active sites and reaction intermediates. Current systems include enzymes involved in antibiotic resistance and pyridoxal-5′-phosphate-dependent chemistry, where protonation and electronic structure play central roles in reactivity.

Our goal is not simply to determine structure, but to connect atomic structure directly to chemical mechanism.

Solid-state NMR can provide atomic-resolution structural and dynamic information for biological systems that are difficult to characterize by conventional solution methods. Our group develops and applies methods for high-resolution and high-sensitivity multidimensional NMR, including approaches for resonance assignment, through-bond and through-space correlation, and characterization of chemical-shift tensors. We make extensive use of high magnetic fields and modern probe technology to extend these measurements to increasingly large and complex proteins. These methods form the experimental foundation for our studies of enzyme structure and mechanism.

A central theme of our work is that molecular models should be tested quantitatively against experiment. First-principles calculations allow us to predict NMR chemical shifts and chemical-shift tensors directly from candidate molecular structures. Comparison with experiment can distinguish structures that differ only subtly in proton positions, tautomeric state, hydrogen bonding, or local geometry.

We are also developing statistical approaches for evaluating competing structural models, including the Uniform Chi-Squared model, and computational tools for visualizing and interpreting NMR tensors.

Together, these methods turn NMR parameters into quantitative restraints on molecular structure.