Assistant Professor, Department of Chemistry and Chemical Biology
Rensselaer Polytechnic Institute

Education:
Ph.D., California Institute of Technology, 2000
B.S., SUNY Fredonia, 1993

Career Highlights:
Prof. Kempf trained in chemical physics with Prof. Dan Weitekamp at Caltech, where he developed optical nuclear magnetic resonance (NMR) methods that he used to image single-electron wavefunctions in structured semiconductor materials. In 2001, he was honored with Caltech’s McCoy award for top doctoral research in chemistry.

Following his graduate work, Dr. Kempf worked for one-year at Cornell with Prof. John Marohn.  There he developed a nanoscale imaging technique using force-detected NMR, an approach that dramatically improves on the sensitivity of the conventional, inductively detected experiment.

Just prior to his arrival at RPI, Dr. Kempf was an NIH Kirchstein postdoctoral fellow at Yale working with Prof. Pat Loria. There, he characterized relations between motional dynamics and the function of large (>50 kDa) protein molecules. Dr. Kempf developed an NMR relaxation experiment that extends the timescale of accessible motions by an order of magnitude in large proteins. Also at Yale, he uncovered the surprising functional significance of motions in the enzyme triosephosphate isomerase that are 10⁴-fold faster than catalysis. This demonstrates that this very fast time scale is an excellent reporter of the enzyme's functional state.

Research Areas:
NMR Study of Biomolecular Dynamics in Chemical Function

The functional behavior of biological macromolecules is often explicable only through motional dynamics and thus requires that we step beyond traditional static perspectives. Elucidating the roles of motion and structural flexibility will move us towards the long-term goals of enhanced therapeutic and commercial exploitation of biochemical processes ranging from enzyme catalysis to signal transduction. The grander goal of mechanistic understanding also requires a powerful, and uncommon, combination of dynamic and structural techniques. In this regard, NMR is the complete package. It delivers near-continuous time resolution across 15 orders of magnitude (ps to hours) and casts that view in a whole-molecule, atomic-resolution structural context.

Our group combines spectroscopic expertise with biochemical insight to understand complex dynamic phenomena in biological macromolecules. Biochemistry and molecular biology are central in this research, while the theories of statistical mechanics, thermodynamics and quantum-mechanical NMR spin evolution are essential for physical interpretation of experimental observations.

Current projects in our group explore the effects of post-translational modifications on protein function, in particular, by testing our hypothesis that these modifications modulate function via motional dynamics. Such intramolecular communication is referred to as allostery, and the study of post-translational modifications as allosteric is unique. We place particular emphasis on glycosylation, the attachment of an oligosaccharide moiety to a protein. Glycosylation is the most frequent and varied of post-translational modifications, and yet it is the least-understood and most-poorly characterized because of the difficulty of glycoprotein production and the complexity of the oligosaccharide. Our group is working to develop new preparatory techniques, as well as dynamic and structural NMR methods that will detail functional variation in these heterogeneous molecules.

• Glycosylation & Allosteric Control in RNase B 
  
  RNase B is a reduced-activity, glycosylated variant of the prototypical enzyme, RNase A. The oligosaccharide is anchored at the non-catalytic residue, Asn34, which is distant from the active site. Thus, the reason for reduced RNase B activity is uncertain. However, motional dynamics play a significant role in RNase A activity and evidence suggests that RNase B is rigidified. This motivates our hypothesis that glycosylation allosterically modulates RNase activity by altering polypeptide dynamics.  NMR relaxation experiments will probe differential RNase A and B dynamics and their relation to function.

• Modulation of Human Adult Hemoglobin (Hb A) by Glycation
  
  Hb A provides the classic example of cooperative behavior often observed among the active sites of multimeric proteins.  In spite of extensive study, several aspects of Hb A activity remain mysterious, but a fresh opportunity for their elucidation is now available. Two mechanisms of O₂ binding cooperativity in Hb A, with either sequential or concerted O₂ binding, identically predict observed behavior. Quantifying solution-state, native motions by dynamic NMR can reveal the true mechanism to yield valuable insight to Hb A’s vital function. In addition, we are interested in modulation of Hb A motion and activity by the ambient chemical addition of glucose. This process, known as glycation, is significant in all adult humans and especially prevalent among diabetics. By characterizing the dynamics of unmodified and glycated Hb A, we aim to understand the deleterious effects of glycation on O₂ transport.

Selected Publications:

Kempf, J.G., Loria, J.P., "Measurement of Intermediate Exchange Phenomena," Chapter 12 (pp181-226) in Protein NMR Techniques, vol. 278, Meth. Molec. Biol., Ed. by K. Downing (Humana Press, Totowa , NJ , 2004).

Kempf J.G., Jung J., Sampson , N.S. , Loria, J.P., "Off-resonance TROSY (R₁ – R_1r) for quantitation of fast exchange in large proteins," J. Amer. Chem. Soc. 125 (40), 12064-5 (2003).

Kempf J.G., Loria J.P., "Protein dynamics from solution NMR – Theory and applications," Cell Biochemistry & Biophysics 37 (3), 187-211 (2003).

Kempf, J.G., Marohn, J.A. “Nanoscale Fourier Transform Imaging with Magnetic Resonance Force Microscopy,” Phys. Rev. Lett. 90 (8), 087601-4 (2003).

Kempf, J.G., Weitekamp, D.P. “Method for atomic-layer-resolved measurement of polarization fields by nuclear magnetic resonance,” J. Vac. Sci. Technol. B 18 (4), 2255-62 (2000).