Photocycle of Sensory Rhodopsin II from Halobacterium salinarum (HsSRII): Mutation of D103 Accelerates M Decay and Changes the Decay Pathway of a 13‐cis O‐like Species

Abstract

Aspartic acid 103 (D103) of sensory rhodopsin II from Halobacterium salinarum (HsSRII, or also called phoborhodopsin) corresponds to D115 of bacteriorhodopsin (BR). This amino acid residue is functionally important in BR. This work reveals that a substitution of D103 with asparagine (D103N) or glutamic acid (D103E) can cause large changes in HsSRII photocycle. These changes include (1) shortened lifetime of the M intermediate in the following order: the wild-type > D103N > D103E; (2) altered decay pathway of a 13-cis O-like species. The 13-cis O-like species, tentatively named Px, was detected in HsSRII photocycle. Px appeared to undergo branched reactions at 0°C, leading to a recovery of the unphotolyzed state and formation of a metastable intermediate, named P370, that slowly decayed to the unphotolyzed state at room temperature. In wild-type HsSRII at 0°C, Px mainly decayed to the unphotolyzed state, and the decay reaction toward P370 was negligible. In mutant D103E at 0°C, Px decayed to P370, while the recovery of the unphotolyzed state became unobservable. In mutant D103N, the two reactions proceeded at comparable rates. Thus, D103 of HsSRII may play an important role in regulation of the photocycle of HsSRII.

Two Consecutive Polar Amino Acids at the End of Helix E are Important for Fast Turnover of the Archaerhodopsin Photocycle

“…The procedure for the extraction of retinal chromophore was according to that previously described in Dai et al . . Briefly, 100 μL of hydroxylamine (1 m ) and 300 μL of methanol were added to a 100 μL solution of He AR or its mutants followed by extraction with 600 μL of hexane.…”

Bacteriorhodopsins extracted from Halobacterium may be useful to absorb cyan and green light (exceptional to reduce scars due to acne ribelle) and couperose

“…The bacteriorhodopsins derived from Halobacterium salinarum is a big protein chain and it has resulted very difficult to find an optimal solubility in cosmetic solvents, but the only one has been an ancient gélée prepared by heating pyrogenic silica in vegetable oil (Sesamum indicum oil) [8][9][10].…”