Application of a sensitive near-field microwave microprobe to the nondestructive characterization of microbial rhodopsin

초록

We study the opto-electrical properties of Natronomonas pharaonis sensory rhodopsin II (NpSRII) by using a near-field microwave microprobe (NFMM) under external light illumination. To investigate the possibility of application of NFMM to biological macromolecules, we used time dependent properties of NPSRII before/after light activation which has three distinct states ground-state, M-state, and O-state. The diagnostic ability of NFMM is demonstrated by measuring the microwave reflection coefficient (S11) spectrum of NpSRII under steady-state illumination in the wavelength range of 350650 nm. Moreover, we present microwave reflection coefficient S11 spectra in the same wavelength range for two fast-photocycling rhodopsins: green light-absorbing proteorhodopsin (GPR) and Gloeobacter rhodopsin (GR). In addition the frequency sweep shift can be detected completely even for tiny amounts of sample (approximate to 103 OD of rhodopsin). Based on these results NFMM shows both very high sensitivity for detecting conformational changes and produces a good time-resolved spectrum. ((c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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