2003 Fifth Annual Beckman Scholars Symposium

"Thermodynamics of Hydrophobic Interactions across a Protein ß-sheet"

Jonathan Spenner
1998 Beckman Scholar Alumni
BA Biological Sciences
Weinberg College of Arts and Sciences
Northwestern University
Presently, Ph.D. Program in Molecular Biophysics
Department of Biophysics and Biophysical Chemistry
The Johns Hopkins University School of Medicine

Interactions between amino acids are crucial for protein folding. To investigate such interactions, a zinc finger-based host-guest system is used. Folded single TFIIIA-like zinc finger peptides contain an anti-parallel ß-sheet and an α-helix but are unfolded in the absence of metal. The host is a model single TFIIIA-like zinc finger peptide, and the guests are valines in two solvent exposed non-hydrogen bonded lateral pairings within the beta-sheet.

Absorption spectroscopy cotitrations were performed to monitor metal binding. An internal standard peptide was included for a competitive assay to maximize precision in metal ion dissociation constant determination. Valines substituted for serine in the two positions had different effects on the deduced folding standard free energy. There is no excess Val-Val ΔΔGº_interaction, and thus contributions from each valine to ΔΔGº_interaction are additive.

Single peptide, single metal titrations using ITC were used to determine the Val-Val ΔΔHº_interaction and to calculate ΔΔSº_interaction. ΔΔHº_interaction is moderately endothermic and ΔΔSº_interaction is favorable. Enthalpic-entropic compensation occurs to achieve zero ΔΔGº_interaction. The release of water is apparently important and gives the favorable entropic contribution.

These thermodynamic results are being compared to the structure of the Val-Val peptide, using NMR of the Zn and Co complexes. The structure of the peptide-Zn complex determined using conventional 2D techniques resulted in a structure without enough constraints to access the interaction between the valine pair. Determination of the paramagnetic susceptibility and residual dipolar coupling tensors of the peptide-Co complex will be used to provide further constraints. The determination of the paramagnetic susceptibility tensor will lead to the addition of constraints from paramagnetic pseudo-dipolar chemical shifts and residual dipolar coupling of the molecule aligned in different fields.

Jon attended Northwestern University after graduating valedictorian from Garber High School in Essexville, Michigan. He received his bachelor’s degree cum laude from Northwestern in June 1999 in biological sciences with a concentration in biochemistry and biophysics and a minor in chemistry. While at Northwestern, Jon also performed research entitled “The effect of N-terminal targeting sequences of varying length on the thermodynamic stability and folding and unfolding kinetics of a mitochondrial precursor protein.” For this research, Jon was awarded the Erwin Macey Scholarship for the Life Sciences from the Weinberg College of Arts and Sciences at Northwestern and the Beckman Scholarship from the Arnold and Mabel Beckman Foundation. Some of the results of this research were published in Nature Structural Biology. Also, Jon received the Merck Index Award for being the top student in organic chemistry, the J. G. Nolan Scholarship and the Captain Maxwell W. Balfour Scholarship for overall superior scholarship at the University, and was repeatedly named to the Dean’s list. From Northwestern, Jon went on to attend the Program in Molecular Biophysics doctoral program at The Johns Hopkins University School of Medicine where he received a Molecular Biophysics NIH Training Grant. He is currently a fourth year student working in the laboratory of Professor Jeremy Berg. His research is entitled “Thermodynamics of Hydrophobic Interactions across a Protein ß-sheet.” He has presented and will present his research at several conferences including the Hopkins Folding Meeting and the Protein Society Symposium and is a member of The Protein Society and the Biophysical Society. Jon looks forward to completing his Ph.D. in May 2004 and publishing his work in the literature. In addition to his research, Jon enjoys reading about statistical physics and partial differential equations, lifting weights, hiking, and traveling. He lives with his wife in Owings Mills, Maryland.