Difference: JamesKempf (21 vs. 22)

Schedule for talk on Oct 21 2009, 1:30 PM NYSBC

Abstract for talk on Oct 21, 2009

• Dynamic, Structural and Electrostatic Insights from NMR Spectroscopy
• Jim Kempf
• Department of Chemistry & Chemical Biology, Rensselaer Polytechnic Institute, Troy, NY 12180

Nuclear Magnetic Resonance (NMR) spectroscopy is well known as powerful probe of biomolecular structure and intramolecular motions. Unique mechanistic insights are available through complementary NMR studies of dynamics and biochemical assays of kinetics. My group has used this approach to explore the influence of glycosylation on the function of RNase A. Glycosylation (i.e., oligosaccharide attachment) is nature’s most frequent modification of proteins. About 50% of human proteins are glycosylated, and yet only a small handful of known protein structures include an oligosaccharide. Furthermore, functional regulation by glycosylation is known but poorly understood. We developed a simple approach to circumvent the challenges preventing widespread NMR studies of glycoproteins. With this, we are exploring the mechanism of glycosylation-induced functional loss in RNase A. Our results show a subtle effect where glycosylation alters intramolecular dynamics that are known to be critical to function of the unmodified enzyme. These are essential steps forward both for application of NMR to glycoproteins and for understanding modes of glycosylation-modulated function.

In a distinct project, we aim to add new capabilities to NMR as a probe of the electrostatic environment within biomolecules. Few methods are available to characterize the intramolecular E fields that govern diverse biochemical processes from photosynthesis to membrane channel transport to enzyme catalysis. Spectral parameters of NMR are unquestionably responsive to electrostatic influence, particularly in the face of the ~10 MV/cm fields common within biomolecules. Unfortunately, applied E fields are impractical beyond ~0.1-1 MV/cm. With that limitation, we predict NMR Stark effects are hopelessly small relative to spectral resolution in the solid state. Thus traditional approaches cannot quantify NMR Stark effects or meet our goal of developing calibrated NMR probes of intramolecular E fields. To overcome this challenge, we provide a POWER (perturbations observed with enhanced resolution) NMR technique that can resolve NMR Stark effects for CO groups at applied E fields of < 0.1 MV/cm. The POWER approach provides needed resolution by removing all spectral contributions other than those from an applied perturbation, e.g., an E field. I will present the first-ever experimental observation of NMR Stark effects in this context, as well as empirical and theoretical progress towards application to carbonyls on the protein backbone and small-molecule protein ligands.