The EF loop in green proteorhodopsin affects conformation and photocycle dynamics.

摘要: The proteorhodopsin family consists of retinal proteins marine bacterial origin with optical properties adjusted to their local environments. For green proteorhodopsin, a highly specific mutation in the EF loop, A178R, has been found cause surprisingly large redshift 20 nm despite its distance from chromophore. Here, we analyze structural and functional consequences this loop by time-resolved spectroscopy solid-state NMR. We that primary photoreaction formation K-like photo intermediate is almost pH-independent slower compared wild-type, whereas decay K-intermediate accelerated, suggesting changes within counterion complex upon mutation. photocycle significantly elongated mainly due an enlarged lifetime late intermediates. Multidimensional MAS-NMR reveals mutation-induced chemical shift propagating chromophore binding pocket, dynamic nuclear polarization-enhanced 13C-double quantum used probe directly retinylidene conformation. Our data show modified interaction network between chromophore, Schiff base, explaining altered kinetic properties. In particular, distorted structure weakens interactions, which help reorienting helix F during reprotonation step photocycle. These lead conclusion plays important role proton uptake cytoplasm but our also reveal clear pathway might be evolutionary conserved communication proteins.