Photochromic bacteriorhodopsin mutant with high holographic efficiency and enhanced stability via a putative self-repair mechanism.

ACS Appl Mater Interfaces
Authors
Keywords
Abstract

The Q photoproduct of bacteriorhodopsin (BR) is the basis of several biophotonic technologies that employ BR as the photoactive element. Several blue BR (bBR) mutants, generated by using directed evolution, were investigated with respect to the photochemical formation of the Q state. We report here a new bBR mutant, D85E/D96Q, which is capable of efficiently converting the entire sample to and from the Q photoproduct. At pH 8.5, where Q formation is optimal, the Q photoproduct requires 65 kJ mol(-1) of amber light irradiation (590 nm) for formation and 5 kJ mol(-1) of blue light (450 nm) for reversion, respectively. The melting temperature of the resting state and Q photoproduct, measured via differential scanning calorimetry, is observed at 100 °C and 89 °C at pH 8.5 or 91 °C and 82 °C at pH 9.5, respectively. We hypothesize that the protein stability of D85E/D96Q compared to other blue mutants is associated with a rapid equilibrium between the blue form E85(H) and the purple form E85(-) of the protein, the latter providing enhanced structural stability. Additionally, the protein is shown to be stable and functional when suspended in an acrylamide matrix at alkaline pH. Real-time photoconversion to and from the Q state is also demonstrated with the immobilized protein. Finally, the holographic efficiency of an ideal thin film using the Q state of D85E/D96Q is calculated to be 16.7%, which is significantly better than that provided by native BR (6-8%) and presents the highest efficiency of any BR mutant to date.

Year of Publication
2014
Journal
ACS Appl Mater Interfaces
Volume
6
Issue
4
Pages
2799-808
Date Published
2014 Feb 26
ISSN
1944-8252
DOI
10.1021/am405363z
PubMed ID
24498928
PubMed Central ID
PMC3985900
Links
Grant list
R01 GM034548 / GM / NIGMS NIH HHS / United States
GM-34548 / GM / NIGMS NIH HHS / United States