Color-tuning of natural variants of heliorhodopsin

• Published in: Scientific reports Vol. 11; no. 1; pp. 854 - 9
• Main Authors: Kim, Se-Hwan, Chuon, Kimleng, Cho, Shin-Gyu, Choi, Ahreum, Meas, Seanghun, Cho, Hyun-Suk, Jung, Kwang-Hwan
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 13-01-2021; Nature Publishing Group; Nature Portfolio
• Subjects: 631/326; 631/45; 631/57; Absorption; Chromophores; Color vision; Homology; Humanities and Social Sciences; Microorganisms; multidisciplinary; Nucleotide sequence; Rhodopsin; Science; Science (multidisciplinary); Site-directed mutagenesis
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-020-72125-0

Microbial rhodopsins are distributed through many microorganisms. Heliorhodopsins are newly discovered but have an unclear function. They have seven transmembrane helices similar to type-I and type-II rhodopsins, but they are different in that the N-terminal region of heliorhodopsin is cytoplasmic. We chose 13 representative heliorhodopsins from various microorganisms, expressed and purified with an N-terminal His tag, and measured the absorption spectra. The 13 natural variants had an absorption maximum (λmax) in the range 530–556 nm similar to proteorhodopsin (λmax = 490–525 nm). We selected several candidate residues that influence rhodopsin color-tuning based on sequence alignment and constructed mutants via site-directed mutagenesis to confirm the spectral changes. We found two important residues located near retinal chromophore that influence λmax. We also predict the 3D structure via homology-modeling of
Thermoplasmatales
heliorhodopsin. The results indicate that the color-tuning mechanism of type-I rhodopsin can be applied to understand the color-tuning of heliorhodopsin.