Structure and Heterogeneity of Retinal Chromophore in Chloride Pump Rhodopsins Revealed by Raman Optical Activity

• DOI: 10.1021/acs.jpcb.3c01801
• Publication Date: 2023-05-18T21:06:27Z
• Authors: Masaiku Ohya; Takashi Kikukawa; Junpei Matsuo; Takashi Tsukamoto; Ryota Nagaura; Tomotsumi Fujisawa; Masashi Unno
• Keywords: Halorhodopsin; Ion pump; Chromophore; Halobacteriaceae

Chloride transport by microbial rhodopsins is actively being researched to understand how light energy converted drive ion pumping across cell membranes. pumps have been identified in archaea and eubacteria, there are similarities differences the active site structures between these groups. Thus, it has not clarified whether a common mechanism underlies pump processes for all chloride-pumping rhodopsins. Here, we applied Raman optical activity (ROA) spectroscopy two chloride pumps, Nonlabens marinus rhodopsin-3 (NM-R3) halorhodopsin from cyanobacterium Mastigocladopsis repens (MrHR). ROA vibrational that provides chiral sensitivity, sign of signals can reveal twisting cofactor molecules within proteins. Our analysis revealed retinal Schiff base NH group orients toward C helix forms direct hydrogen bond with nearby NM-R3. In contrast, MrHR suggested contain conformations twisted opposite directions; one conformation like NM-R3, while other water molecule anchored G residue. These results suggest general which "dragged" flipping upon photoisomerization.