Anabaena sensory rhodopsin is a light-driven unidirectional rotor

The implementation of multiconfigurational quantum chemistry methods into a quantum-mechanics/molecular-mechanics protocol has allowed the construction of a realistic computer model for the sensory rhodopsin of the cyanobacterium Anabaena PCC 7120. The model, which reproduces the absorption spectra of both the all-trans and 13-cis forms of the protein and their associated K and L intermediates, is employed to investigate the light-driven steps of the photochromic cycle exhibited by the protein. It is found that the photoisomerizations of the all-trans and 13-cis retinal chromophores occur through unidirectional, counterclockwise 180 deg rotations of the =C14-C15= moiety with respect to the Lys210-linked end of the chromophore axis. Thus, the sequential interconversions of the all-trans and 13-cis forms during a single photochromic cycle yield a complete (360 deg) unidirectional rotation of the =C14-C15= moiety. This finding implies that Anabaena sensory rhodopsin is a biological realization of a light-driven molecular rotor.
Original Publication:Angela Strambi, Bo Durbeej, Nicolas Ferre and Massimo Olivucci, Anabaena sensory rhodopsin is a light-driven unidirectional rotor, 2010, Proceedings of the National Academy of Sciences of the United States of America, (107), 50, 21322-21326.http://dx.doi.org/10.1073/pnas.1015085107Copyright: National Academy of Sciences; 1999http://www.nas.edu