Terahertz Spectroscopy of Bacteriorhodopsin and Rhodopsin; Similarities and Differences
R. Balu 1, H. Zhang 1, E. Zukowski 1, J.-Y. Chen 2, A. G. Markelz 2 and Susan K. Gregurick 3*
1 UMBC
2 University at Buffalo
3 University of Maryland, Baltimore County
* To whom correspondence should be addressed. E-mail: greguric{at}umbc.edu.
Submitted on January 25, 2007
Revised on March 19, 2007
Accepted on 19 November 2007
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Abstract |
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We have studied the low frequency terahertz spectroscopy of two photoactive protein systems, rhodopsin and bacteriorhodopsin, as a means to characterize collective low frequency motions in helical transmembrane proteins. From this work we have found that the nature of the vibrational motions activated by terahertz radiation are surprisingly similar between these two structurally similar proteins. Specifically, at the lowest frequencies probed, the cytoplasmic loop regions of the proteins are highly active and at the higher terahertz frequencies studied the extracellular loop regions of the protein systems become vibrationally activated. In the case of bacteriorhodopsin the calculated terahertz spectra are compared with the experimental terahertz signature. This work illustrates the importance of terahertz spectroscopy to identify vibrational degrees of freedom which correlate to known conformational changes in these proteins.
Key Words:
bacteriorhodopsin, conformational analysis, normal mode analysis, rhodopsin, terahertz spectroscopy
