Study of the Molecular Mechanism of W182 in the Bacteriorhodopsin Photocycle
East China Normal University, School of Physics and Materials Science, Shanghai Key Laboratory of Magnetic Resonance, Shanghai, 200062, China
Molecular Microbiology Research, 2020, Vol. 10, No. 3
Received: 06 Jun., 2020 Accepted: 09 Jun., 2020 Published: 09 Jun., 2020
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This article was first published in Genomics and Applied Biology in Chinese, and here was authorized to translate and publish the paper in English under the terms of Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Bacteriorhodopsin (bR), a seven-transmembrane photoreceptor protein with retinal as the chromophore found in purple membrane of Halobacterium salinarum R1M1, functions as a proton pump. Tryptophan 182 (W182), one of the most conserved aromatic residues within the microbial rhodopsin family proteins, locates in the intracellular side of the retinal binding pocket and plays a very important role in affecting the photocycle and proton pumping activity of bR through the interaction with the retinal polyene chain. In this study, site-directed mutagenesis of W182F and W182A, in combination with in-situ UV-vis absorption spectroscopy, light-induced transient absorption change sepectroscopy, pH titration and molecular dynamics simulations, is employed to elaborate the molecular mechanism the functional role of W182 in the bR photocycle. Our results show that perturbation of W182F to the bR photocycle mainly originates from the disturbance of the retinal binding pocket, while the affect by the mutation of W182A mainly comes from the disruption of the intracellular half-channel of proton translocation pathway. The two mutations have different molecular mechanisms on the effect of proton transport on the extracellular half channel, resulting in a significant difference in the decay of M intermediate state.
Bacteriorhodopsin; Tryptophan 182; Site-directed mutation; Photointermediates; Molecular mechanism
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Molecular Microbiology Research
• Volume 10