Functional roles of tyrosine 185 during the bacteriorhodopsin photocycle as revealed by in situ spectroscopic studies

Xiaoyan Ding; Chao Sun; Haolin Cui; Sijin Chen; Yujiao Gao; Yanan Yang; Juan Wang; Xiao He; Dinu Iuga; Fang Tian; Anthony Watts; Xin Zhao

doi:10.1016/j.bbabio.2018.05.011

Functional roles of tyrosine 185 during the bacteriorhodopsin photocycle as revealed by in situ spectroscopic studies

Biochim Biophys Acta Bioenerg. 2018 Oct;1859(10):1006-1014. doi: 10.1016/j.bbabio.2018.05.011. Epub 2018 May 23.

Authors

Xiaoyan Ding¹, Chao Sun², Haolin Cui², Sijin Chen², Yujiao Gao², Yanan Yang², Juan Wang², Xiao He³, Dinu Iuga⁴, Fang Tian⁵, Anthony Watts⁶, Xin Zhao⁷

Affiliations

¹ Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, East China Normal University, Shanghai 200062, PR China; Department of Biochemistry and Molecular Biology, Penn State College of Medicine, PA 17033-0850, USA.
² Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, East China Normal University, Shanghai 200062, PR China.
³ Shang Engineering Research Center of Molecular Therapeutics and New Drug Development, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, PR China.
⁴ The UK 850 MHz Solid-State NMR Facility, Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
⁵ Department of Biochemistry and Molecular Biology, Penn State College of Medicine, PA 17033-0850, USA. Electronic address: ftian@psu.edu.
⁶ Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK. Electronic address: anthony.watts@bioch.ox.ac.uk.
⁷ Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, East China Normal University, Shanghai 200062, PR China. Electronic address: xzhao@phy.ecnu.edu.cn.

PMID: 29800547
DOI: 10.1016/j.bbabio.2018.05.011

Abstract

Tyrosine 185 (Y185), one of the aromatic residues within the retinal (Ret) chromophore binding pocket in helix F of bacteriorhodopsin (bR), is highly conserved among the microbial rhodopsin family proteins. Many studies have investigated the functions of Y185, but its underlying mechanism during the bR photocycle remains unclear. To address this research gap, in situ two-dimensional (2D) magic-angle spinning (MAS) solid-state NMR (ssNMR) of specifically labelled bR, combined with light-induced transient absorption change measurements, dynamic light scattering (DLS) measurements, titration analysis and site-directed mutagenesis, was used to elucidate the functional roles of Y185 during the bR photocycle in the native membrane environment. Different interaction modes were identified between Y185 and the Ret chromophore in the dark-adapted (inactive) state and M (active) state, indicating that Y185 may serve as a rotamer switch maintaining the protein dynamics, and plays an important role in the efficient proton-pumping mechanism in the bR purple membrane.

Keywords: Dark-adapted state and M state; Photocycle; Proton pumping; Retinal chromophore; Tyrosine 185.