Poster abstracts

Poster number 30 submitted by Ting-fang He

Ultrafast short-range electron transfer dynamics in biology

Ting-fang He (Ohio State Biochemistry Program, The Ohio State University), Lijun Guo (Department of Physics, The Ohio State University), Dongping Zhong (Department of Physics, The Ohio State University)

Abstract:
Studies led to elucidate the molecular mechanisms of the photoinduced electron transfer processes which are central to many biological functions such as photosynthesis and DNA repair, are of great importance. With the integration of site-directed mutagenesis and femtosecond-resolved spectroscopy, we present here the systematic studies of ultrafast dynamics of an electron-transfer cycle, forward and backward, in a biological model system of D. vulgaris flavodoxin in both oxidized and semiquinone state. Upon excitation of flavin prosthetic cofactor which acts as an electron acceptor, the transient intermediates from the stacking (3~4 Å) aromatic donors, the cationic tryptophan and tyrosine radical, were captured. The completion of the single electron-transfer cycle was determined to be on the order of several to tens of picoseconds. In the oxidized flavodoxin, highly favorable redox potential drives the forward electron transfer to the ultrafast while the backward was characterized being correlated with the local protein solvation in several picoseconds. The entity of the local solvation at present is interpreted to enhance the return dynamics and close the cycle. On the contrary, this exploitation of the local protein solvation appears invisible in the semiquinone flavodoxin since the return dynamics is already well optimized with proper reorganization energy by the local structure, resulting in the order of subpicosecond timescale, more than ten times faster than its forward. The comparatively slower forward was also observed strongly correlated with the concomitant local solvation. We propose that, in addition to the redox potential, proteins manipulate electron transfer dynamics over distances smaller than 10 Å through the local solvation. This finding will provide a molecular basis to explore the fundamentals of protein electron transfer over a short distance, and is critical to uncovering the biological control.

Keywords: femtosecond dynamics, intraprotein electron transfer, flavodoxin