(Invited Paper) Why is THz Sensitive to Protein Functional States? Oxidation State of Cytochrome C

Yunfen He ¹, J.-Y. Chen ², J. R. Knab ³, Wenjun Zheng ¹ and A. G. Markelz ^1*
1 Physics Department, University at Buffalo, SUNY, Buffalo, NY 14260
² Washington State University, Pullman, WA
³ Technical Univeristy of Delft, Delft, Netherlands
^*1 E-mail: amarkelz@acsu.buffalo.edu

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Abstract: We investigate the presence of structural collective motions on a picosecond time scale for the heme protein, cytochrome c, as a function of oxidation and hydration, using terahertz (THz) time-domain spectroscopy and molecular dynamics simulations. Structural collective mode frequencies have been calculated to lie in this frequency range, and the density of states can be considered a measure of flexibility. A dramatic increase in the THz response occurs with oxidation, with the largest increase for lowest hydrations and highest frequencies. For both oxidation states the measured THz response rapidly increases with hydration saturating above ~25% (g H₂O/g protein), in contrast to the rapid turn-on in dynamics observed at this hydration level for other proteins. Quasi-harmonic collective vibrational modes and dipole-dipole correlation functions are calculated from the molecular dynamics trajectories. The collective mode density of states alone reproduces the measured hydration dependence providing strong evidence of the existence of these collective motions. The large oxidation dependence is reproduced only by the dipole-dipole correlation function, indicating the contrast arises from diffusive motions consistent with structural changes occurring in the vicinity of a buried internal water molecule.

Keywords: Structural collective motions, Terahertz, Molecular dynamics, Heme protein, Cytochrome c.

Received: 2010-7-2

Published: 2010-12-31

Acknowledgments: This work was supported by ARO grant DAAD 19-02-1-0271, ACS grant PRF 39554-AC6, NSF CAREER grant PHY-0349256, NSF REU grant DMR-0243833 and NSF IGERT grant DGE0114330.

Cite this article:
Yunfen He, J.-Y. Chen, J. R. Knab, Wenjun Zheng, and A. G. Markelz. (Invited Paper) Why is THz Sensitive to Protein Functional States? Oxidation State of Cytochrome C[J]. International Journal of Terahertz Science and Technology, 2010, Vol.3, No.4: 149-162.  DOI:10.11906/TST.149-162.2010.12.15

URL: http://www.tstnetwork.org/10.11906/TST.149-162.2010.12.15