A conserved Trp residue in HwBR contributes to its unique tolerance toward acidic environments
Journal
Biophysical journal
Journal Volume
121
Journal Issue
16
Pages
3136-3145
Date Issued
2022-08-16
Author(s)
Abstract
Bacteriorhodopsin (BR) is a light-driven outward proton pump found mainly in halophilic archaea. A BR from an archaeon Haloquadratum walsbyi (HwBR) was found to pump protons under more acidic conditions compared with most known BR proteins. The atomic structural study on HwBR unveiled that a pair of hydrogen bonds between the BC and FG loop in its periplasmic region may be a factor in such improved pumping capability. Here, we further investigated the retinal-binding pocket of HwBR and found that Trp94 contributes to the higher acid tolerance. Through single mutations in a BR from Halobacterium salinarum and HwBR, we examined the conserved tryptophan residues in the retinal-binding pocket. Among these residues of HwBR, mutagenesis at Trp94 facing the periplasmic region caused the most significant disruption to optical stability and proton-pumping capability under acidic conditions. The other tryptophan residues of HwBR exerted little impact on both maximum absorption wavelength and pH-dependent proton pumping. Our findings suggest that the residues from Trp94 to the hydrogen bonds at the BC loop confer both optical stability and functionality on the overall protein in low-pH environments.
Subjects
TRYPTOPHAN RESIDUES; 9-METHYL GROUP; SCHIFF-BASE; BACTERIORHODOPSIN; SUBSTITUTIONS; HELIX; ULTRAVIOLET; PHOTOCYCLE; SYSTEM
Publisher
CELL PRESS
Type
journal article