Reversible inhibition of proton release activity and the anesthetic-induced acid-base equilibrium between the 480 and 570 nm forms of bacteriorhodopsin

Abstract

In purple membrane added with general anesthetics, there exists an acid-base equilibrium between two spectral forms of the pigment: bR570 and bR480 (apparent pKa = 7.3). As the purple 570 nm bacteriorhodopsin is reversibly transformed into its red 480 nm form, the proton pumping capability of the pigment reversibly decreases, as indicated by transient proton release measurements and proton translocation action spectra of mixture of both spectral forms. It happens in spite of a complete photochemical activity in bR480 that is mostly characterized by fast deprotonation and slow reprotonation steps and which, under continuous illumination, bleaches with a yield comparable to that of bR570. This modified photochemical activity has a correlated specific photoelectrical counterpart: a faster proton extrusion current and a slower reprotonation current. The relative areas of all photocurrent phases are reduced in bR480, most likely because its photochemistry is accompanied by charge movements for shorter distances than in the native pigment, reflecting a reversible inhibition of the pumping activity.

Directed evolution of bacteriorhodopsin for applications in bioelectronics

“…At the time, interest in pursuing bioelectronic devices was tied to military development and international competition towards designing new nanobiotechnologies, which had first elicited a holographic processor based on BR thin films through the project, Biochrome [80,81]. In the subsequent decades of research, BR has emerged as one of the most rigorously investigated biomaterial for use in electronic applications, culminating in the development of numerous prototypes of devices that include Fouriertransform holographic associative processors [25,42,[82][83][84], three-dimensional optical memories [25,82,85,86], biosensors [87,88], photovoltaic cells [89][90][91] and protein-based retinal prostheses [28,92]. Recent advances in genetic engineering and directed evolution have further invigorated the pursuit of optimizing these protein-based devices, thereby increasing the potential of introducing a commercial BR-based technology in the near future [38,41,76].…”

Discovery of bacteriorhodopsins in Haloarchaeal species isolated from Indian solar salterns: deciphering the role of the N‐terminal residues in protein folding and functional expression

“…BR can remain in the Q state for 7 to 12 years and then returns to its normal bR state upon red photon illumination (Stuart et al ., , ). These unique features coupled with high stability make BR a versatile biological material with numerous potential attractive applications in photovoltaic cells (Hong, ; Xu et al ., ; Chellamuthu et al ., ), artificial retina (Chen and Birge, ; Cutsuridis and Wennekers, ), biosensors (Boucher et al ., ; Lanyi and Luecke, ), optical memory storage devices (Birge et al ., , ; Stuart et al ., , ) and optogenetics (Lindvold and Lausen, ; Fábián et al ., ). Several attempts to recombinantly express H. salinarum BR using E. coli as a host have been reported.…”

Interaction of the general volatile anesthetic Enflurane with bacteriorhodopsin-DPPC proteoliposomes

“…It thus enables to assess the anesthetic incorporation into the lipid phase of proteoliposomes at any temperature. On another hand, in a concentration-dependent manner, Enflurane induces a large spectral transition in bacteriorhodopsin, shifting its k max from 570 to 480 nm [7]. Both phenomena are sketched in Fig.…”

“…In the presence of the anesthetic, this protein, contained in the purple patches of halobacteria, is converted from its purple form (k max 570 nm) to a red form (k max 480 nm) and its proton pumping activity is inhibited [7][8][9]. DPPC is particularly suitable for reconstitution of bacteriorhodopsin in artificial membranes as, among a homologous series of acyl chains phosphatidyl cholines, it is the one whose physical state is less perturbed by the presence of bacteriorhodopsin [10,11].…”