Unusual Photoisomerization Pathway in a Near-Infrared Light Absorbing Enzymerhodopsin

Microbial and animal rhodopsins possess retinal chromophores which capture light and normally photoisomerize from all-trans to 13-cis and from 11-cis to all-trans-retinal, respectively. Here, we show that a near-infrared light-absorbing enzymerhodopsin from Obelidium mucronatum (OmNeoR) contains the all-trans form in the dark but isomerizes into the 7-cis form upon illumination. The photoproduct (lambda(max )= 372 nm; P-372) possesses a deprotonated Schiff base, and the system exhibits a bistable nature. The photochemistry of OmNeoR was arrested at < 270 K, indicating the presence of a potential barrier in the excited state. Formation of P-372 is accompanied by protonation changes of protonated carboxylic acids and peptide backbone changes of an alpha-helix. Photoisomerization from the all-trans to 7-cis retinal conformation rarely occurs in any solvent and protein environments; thus, the present study reports on a novel photochemistry mediated by a microbial rhodopsin, leading from the all-trans to 7-cis form selectively.

Automated summary

This study reports on a novel photochemistry mediated by a microbial rhodopsin, which selectively transforms the all-trans form to the 7-cis form. The reaction occurs in the dark with the all-trans form, but isomerizes into the 7-cis form upon illumination, accompanied by changes in protein structure and protonation.