Mutations of Conserved Tryptophans in the Retinal Binding Pocket Contribute Differently upon Acid-tolerance in Two Different Bacteriorhodopsins

Autor: Hong-Syuan Lin, 林宏軒
Rok vydání: 2018
Druh dokumentu: 學位論文 ; thesis
Popis: 106
Rhodopsins belong to a family of retinal-binding protein (RBP) which are widely distributed in different light sensitive organs. In microbes, rhodopsin are distributed on cell membrane, and they respond to light stimuli to mediate various physical functions. This protein family has a conserved seven-transmembrane domain with a retinal binding to a conserved lysine on the seventh helix. Retinal is further stabilized by highly conserved surrounding aromatic amino acids to form a retinal binding pocket, RBP. Bacteriorhodopsin (BR) is a light-driven outward proton pump found in haloarchaea, Upon light activation, BR pump a proton out of cell per photocycle to provide proton gradient to further ATP via F1Fo ATP synthase. Previous mutagenesis study in a well-studied bacteriorhodopsin, HsBR, showed that some residues in RBP can affect chromophore stability and the maximum absorbance (Abs-max). Among these residues, tryptophan residues were shown to play important roles in interaction with retinal and the Abs-max wavelength. Previously we found HwBR, a bacteriorhodopsin from Haloquadratum walsbyi, to have more stable Abs-max and functionality under acidic condition when compared to HsBR even though they have identical residues in RBP. To investigate such a paradox, this study mutated three corresponding tryptophan residues in both BR proteins and found conserved tryptophans contributed differently to the Abs-max and functionality under acidic conditions in two BR. We concluded further analysis in the interaction between tryptophan and nearby residues or water molecule network essential. This study also provide clear clues for future investigating on the acid-tolerance of RBP in microbial rhodopsin.
Databáze: Networked Digital Library of Theses & Dissertations
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