This Article Full Text Full Text (PDF) All Versions of this Article: biophysj.107.105163v1 94/8/3217    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Balu, R. Articles by Gregurick, S. K. PubMed PubMed Citation Articles by Balu, R. Articles by Gregurick, S. K.

Terahertz Spectroscopy of Bacteriorhodopsin and Rhodopsin: Similarities and Differences

R. Balu ^*, H. Zhang ^*, E. Zukowski ^*, J.-Y. Chen , A. G. Markelz  and S. K. Gregurick ^*

^* Department of Chemistry and Biochemistry, University of Maryland, Baltimore, Maryland 21250; and Department of Physics, University at Buffalo, Buffalo, New York 14260

Correspondence: Address reprint requests to Susan K. Gregurick, E-mail: greguric{at}umbc.edu.

We 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 found that the nature of the vibrational motions activated by terahertz radiation is 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.