Research Summary:

Biomolecules form a class of complex systems that are fundamental to the existence of life. We study the structure and dynamics of such systems in order to better understand the microscopic aspects of their crucial and varied functions. We use a variety of optical-based methods such as inelastic (Raman) and quasi-elastic (Rayleigh) laser light scattering, as well as the complementary techniques of femtosecond coherence, infrared, and ultraviolet absorption spectroscopies, to probe heme containing proteins (e.g. hemoglobin, myoglobin, cytochrome c, cytochrome P450, chloroperoxidase, horseradish peroxidase, nitrophorin, cystathione beta synthase). Resonance effects are exploited by tuning the laser frequency to energies ~1-4 eV that coincide with the electronic excitations of 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.

Additional experiments utilize pulsed laser excitation and allow time-resolved dynamic information to be obtained. In particular, unstable catalytic intermediates involving enzyme-substrate complexes are being studied using sophisticated optical detection systems, which are gated to accept short bursts of scattered light over broad spectral regions. High resolution transient absorption studies are also being used to characterize kinetic 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. Other experiments involve studies of photon induced perturbations, such as photoreduction and local chromophore heating, which are important in understanding photon-induced biological processes involving isomerization, charge separation, and energy transport.

The laboratory has the capability of following the dynamics of biomolecular systems on femtosecond to millisecond timescales. Current studies are focusing on the technique of "vibrational coherence spectroscopy" which has allowed us to detect 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.

Recent Publications:

Paul M. Champion, "Following the Flow of Energy in Biomolecules," Science 310, 980 (2005)

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).

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).

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, Dan Ionascu, Minoru Kubo, Xiong Ye, John Dawson, Robert L Osborne, S. G. Sligar, Ilia Denisov, Aditi Das, T. L. Poulos, James Terner and Paul M. Champion, "Low Frequency Dynamics of Caldariomyces fumago Chloroperoxidase Probed by Femtosecond Coherence Spectroscopy", Biochemistry 47, 5156-5167 (2008).

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