CPM Seminar

Spectral Hole Burning, Recovery and Thermocycling in Chlorophyll-Protein Complexes: Distributions of Barriers on the Protein Energy Landscape

Valter Zazubovits

Concordia University

I will present some recent results on applying spectral hole burning technique to exploring energy landscapes in protein-chlorophyll complexes. An introduction to spectral hole burning will be offered, and I will discuss relationships between information obtained via spectral hole burning and via single molecule (or single complex) spectroscopy. In particular, we will report on the progress towards developing unified model simultaneously describing both hole burning and hole recovery, at fixed temperature and upon thermocycling. Our research focuses on a CP43 antenna complex of Photosystem II. The distributions of the tunneling parameter λ and barrier height V have been determined for this complex, for both excited and ground states of the pigment/protein system. These parameters likely describe two distinct tiers of its protein energy landscape. We demonstrate that the distributions actually contributing to spectral hole recovery differ, quantitatively and in some cases qualitatively, from the whole true barrier (or λ-) distributions. This allows us to confirm that Gaussian distribution of the tunneling parameter λ is most appropriate for describing the “burnable” protein energy landscape tier. The issue of the shape of the barrier distribution has important implications in physics of amorphous solids at low temperatures, as most widespread theories suggest that barrier distribution is inversely proportional to square root of the barrier height (which corresponds to uniform distribution of tunneling parameter).

Time permitting, I may discuss also other factors affecting spectral hole burning in pigment-protein complexes, for instance distributions of excitation energy transfer rates.