%0 Conference Proceedings %B Mater. Res. Soc. Symp. %D 2004 %T Terahertz measurements of the Photoactive Protein Bacteriorhodopsin mutant D96N: M and P states %A Chen, C.-Y. %A Knab, J. R. %A Cerne, J. %A Hillebrecht, J. R. %A Birge, R. R. %A Markelz, A. G. %X

We use terahertz (THz) spectroscopy as a biomaterials characterization tool. Previously we have shown a strong contrast between the THz dielectric response for wild type (WT) and D96N mutant of bacteriorhodopsin. In those studies we observed a large increase in the THz absorbance of WT with excitation to thermally captured photo-intermediates whereas no such increase in absorbance was observed for the mutant D96N. These results suggest that the THz response is sensitive to structural changes and relative flexibility of biomolecules. However the photo-intermediate populations of the WT and D96N samples were not equivalent in those measurements. While the WT samples had relaxed (bR), M and P state intermediates present, the D96N samples had only bR and M states. Here we present terahertz absorbance measurements of D96N as a function of M and P state populations at room temperature. The THz response is constant for intermediate states populations up to 23% M state and up to 30% P state. These results verify that there is a fundamental difference in the conformational dynamics as measured by THz dielectric response for a single residue mutation.

%B Mater. Res. Soc. Symp. %S in Proteins as Materials (ed. V. P. Conteicello, et al) %C Warrendale, PA %V 826 %P pages261–267 %G eng %R 10.1557/PROC-826-V2.6 %0 Journal Article %J Biophysical Journal %D 2003 %T Protein flexibility and conformational state: A comparison of collective vibrational modes of wild-type and D96N bacteriorhodopsin %A Whitmire, S. E. %A Wolpert, D. %A Markelz, A. G. %A Hillebrecht, J. R. %A Galan, J. %A Birge, R. R. %K angstrom resolution %K Biophysics %K dna %K films %K frequency %K harmonic-analysis %K inelastic neutron-scattering %K large systems %K mixed basis %K normal-modes %K purple membranes %K structural-changes %K transform infrared-spectroscopy %X

Far infrared ( FIR) spectral measurements of wild-type (WT) and D96N mutant bacteriorhodopsin thin films have been carried out using terahertz time domain spectroscopy as a function of hydration, temperature, and conformational state. The results are compared to calculated spectra generated via normal mode analyses using CHARMM. We find that the FIR absorbance is slowly increasing with frequency and without strong narrow features over the range of 2-60 cm(-1) and up to a resolution of 0.17 cm(-1). The broad absorption shifts in frequency with decreasing temperature as expected with a strongly anharmonic potential and in agreement with neutron inelastic scattering results. Decreasing hydration shifts the absorption to higher frequencies, possibly resulting from decreased coupling mediated by the interior water molecules. Ground-state FIR absorbances have nearly identical frequency dependence, with the mutant having less optical density than the WT. In the M state, the FIR absorbance of the WT increases whereas there is no change for D96N. These results represent the first measurement of FIR absorbance change as a function of conformational state.

%B Biophysical Journal %V 85 %P 1269-1277 %8 Aug %@ 0006-3495 %G English %9 Article %M WOS:000184428300052 %R 10.1016/S0006-3495(03)74562-7 %0 Conference Proceedings %B Ultrafast Phenomena in Semiconductors VII %D 2003 %T Ultrafast THz spectroscopy of photoactive biomolecules %A Chen, J.-Y. %A Whitmire, S. E. %A Markelz, A. G. %A Hillebrecht, J. R. %A Birge, R. R. %B Ultrafast Phenomena in Semiconductors VII %C San Jose, California %P 146-153 %8 01/2003 %G eng %0 Conference Proceedings %B Proceedings of the 26th International Conference on Infrared and Millimeter Waves %D 2001 %T Terahertz Time domain spectroscopy of the M intermediate state of Bacteriorhodopsin %A Whitmire, S. %A Markelz, A. G. %A Hillebrecht, J. R. %A Birge, R. R. %B Proceedings of the 26th International Conference on Infrared and Millimeter Waves %C Toulouse, France %P 345-348 %8 09/2001 %G eng