Experimental Biological Physics
Physics Department Chair and IPL Director
PhD University of Illinois at Urbana-Champaign, 1975
Biomolecules form a class of complex systems that are fundamental to the existence of life. We study the structure and dynamics of such biomolecules using a variety of ultrafast laser-based techniques such as vibrational coherence spectroscopy (VCS) and broadband pump-probe kinetics that occur on femtosecond to millisecond timescales. We also use more traditional techniques such as resonance Raman scattering and we are developing new methodologies, such as femtosecond stimulated Raman scattering. The latter method has excellent time and frequency resolution and it can be used as a spectroscopic probe of individual biomolecules as well as a method for imaging biological tissue and cells.
Time-resolved dynamic information helps us to probe biochemical reaction coordinates as well as unstable catalytic intermediates that involve enzyme-substrate complexes. The vibrational coherence measurements are designed to probe very low frequency motions, which have energies that can be thermally excited. Such motions are used by biomolecules to extract energy from the environment in order to do useful biochemical work. The kinetic studies characterize processes taking place over a wide dynamic range of timescales. These processes involve diatomic ligand binding, rapid (local) structural relaxations, and more global protein conformational interconversions. Much of our work involves studies of heme containing proteins, which have roles in oxygen storage, electron transport, signaling and catalysis. Photoactive molecules, such as the green fluorescent protein, are also studied in order to better understand the fundamental aspects of proton transport in biological systems.
We often use resonance enhancement and tune the laser frequency to energies ~1-4 eV that coincide with the electronic excitations of the various biological chromophores. In the case of Raman scattering, the resonance enhancement effects are enormous and allow us to selectively interrogate specific regions within the complex biological macromolecule. Measurements of absolute scattering cross-sections and the intensity of the scattering as a function of excitation frequency are used to obtain the electron-nuclear coupling parameters as well as other information pertinent to the structure and function of these materials. Samples are studied in the solution, crystalline and frozen states.
Current studies are focusing on the techniques of femtosecond Stimulated Raman Scattering (FSRS) and “vibrational coherence spectroscopy” (VCS) which allow us to better understand the very interesting, functionally important, low frequency biomolecular oscillations. Current work is focused on disentangling the structural and dynamic information that is contained in these novel experiments.
Venugopal Karunakaran, Ilia Denisov, Stephen G. Sligar, Paul M. Champion, “Investigation of the low frequency dynamics of heme proteins: Native and mutant cytochrome P450cam and redox partner complexes”, J. Phys. Chem. B 115, 5665-5677 (2011).
Abdelkrim Benabbas, Xiong Ye, Minoru Kubo, Zhenyu Zhang, Estelle M.Maes, William R. Montfort, Paul M. Champion, “Ultrafast Dynamics of Diatomic Ligand Binding to Nitrophorin 4”, J. Am. Chem. Soc. 132, 2811-2820 (2010).
Zhenyu Zhang, Abdelkrim Benabbas, Xiong Ye, Anchi Yu, and Paul M. Champion, “Measurements of Heme Relaxation and Ligand Recombination in Strong Magnetic Fields”, J. Phys. Chem. B 113, 10923-10933 (2009).
Flaviu Gruia, Minoru Kubo, Xiong Ye, Dan Ionascu, Changyuan Lu, Robert K. Poole, Syun-Ru Yeh, and Paul M. Champion, “Coherence Spectroscopy Investigations of the Low-frequency Vibrations of Heme: Effects of Protein-specific Perturbations”, J. Am. Chem. Soc. 130, 5231-5244. (2008).
Flaviu Gruia, Minoru Kubo, Xiong Ye and Paul M. Champion, “Investigations of vibrational coherence in the low frequency region of ferric heme proteins”, Biophys. J. 94, 2252-2268 (2008).
Xiong Ye, Dan Ionascu, Florin Gruia, Anchi Yu, Abdelkrim Benabbas, and Paul M. Champion, “Temperature Dependent Heme Kinetics with Nonexponential Binding and Barrier Relaxation in the Absence of Protein Conformational Substates”, Proc. Nat. Acad. Sci. 104, 14682 (2007).