Open AccessInsights into the Protein Functions and Absorption Wavelengths of Microbial Rhodopsins
Author(s) -
Masaki Tsujimura,
Hiroshi Ishikita
Publication year - 2020
Publication title -
the journal of physical chemistry. b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 392
eISSN - 1520-6106
pISSN - 1520-5207
DOI - 10.1021/acs.jpcb.0c08910
Subject(s) - rhodopsin , bacteriorhodopsin , absorption (acoustics) , schiff base , counterion , chemistry , wavelength , biophysics , absorption spectroscopy , retinal , photochemistry , crystallography , ion , biochemistry , biology , optics , membrane , organic chemistry , physics
Using a quantum mechanical/molecular mechanical approach, the absorption wavelength of the retinal Schiff base was calculated based on 13 microbial rhodopsin crystal structures. The results showed that the protein electrostatic environment decreases the absorption wavelength significantly in the cation-conducting rhodopsin but only slightly in the sensory rhodopsin. Among the microbial rhodopsins with different functions, the differences in the absorption wavelengths are caused by differences in the arrangement of the charged residues at the retinal Schiff base binding moiety, namely, one or two counterions at the three common positions. Among the microbial rhodopsins with similar functions, the differences in the polar residues at the retinal Schiff base binding site are responsible for the differences in the absorption wavelengths. Counterions contribute to an absorption wavelength shift of 50-120 nm, whereas polar groups contribute to a shift of up to ∼10 nm. It seems likely that protein function is directly associated with the absorption wavelength in microbial rhodopsins.