Removal of the Transducer Protein from Sensory Rhodopsin I Exposes Sites of Proton Release and Uptake During the Receptor Photocycle
Overview
Authors
Affiliations
The phototaxis receptor sensory rhodopsin-I (SR-I) was genetically truncated in the COOH terminus which leads to overexpression in Halobacterium salinarium and was expressed in the presence and absence of its transducer, HtrI. Pyranine (8-hydroxyl-1,3,6-pyrene-trisulfonate) was used as a pH probe to show that proton release to the bulk phase results from the SR-I587 to S373 photoconversion, but only in the absence of transducer. The stoichiometry is 1 proton/S373 molecule formed. When SR-I is overexpressed in the presence of HtrI, the kinetics of the thermal return of S373 to SR-I587 is biphasic. A kinetic dissection indicates that overexpressed SR-I is present in two pools: one pool which generates an SR-I molecule possessing a normal (i.e., transducer-interacting) pH-independent rate of S373 decay, and a second pool which shows the pH-dependent kinetics of transducer-free S373 decay. The truncated SR-I receptor functions normally based on the following criteria: (i) Truncated SR-I restores phototaxis (attractant and repellent responses) when expressed in a strain lacking native SR-I, but containing HtrI. (ii) The absorption spectrum and the flash-induced absorption difference spectrum are indistinguishable from those of native SR-I. (iii) The rate of decay of S373 is pH-dependent in the absence of HtrI but not in the presence of HtrI. The data presented here indicate that a proton-conducting path exists between the protonated Schiff base nitrogen and the extramembranous environment in the transducer-free receptor, and transducer binding blocks this path.
Chen J, Lin Y, Fu H, Yang C Sci Rep. 2019; 9(1):5672.
PMID: 30952934 PMC: 6450946. DOI: 10.1038/s41598-019-42193-y.
Mechanism divergence in microbial rhodopsins.
Spudich J, Sineshchekov O, Govorunova E Biochim Biophys Acta. 2013; 1837(5):546-52.
PMID: 23831552 PMC: 3844102. DOI: 10.1016/j.bbabio.2013.06.006.
A Schiff base connectivity switch in sensory rhodopsin signaling.
Sineshchekov O, Sasaki J, Phillips B, Spudich J Proc Natl Acad Sci U S A. 2008; 105(42):16159-64.
PMID: 18852467 PMC: 2571000. DOI: 10.1073/pnas.0807486105.
Sineshchekov O, Spudich E, Trivedi V, Spudich J Biophys J. 2006; 91(12):4519-27.
PMID: 17012323 PMC: 1779924. DOI: 10.1529/biophysj.106.093641.
The photoreceptor sensory rhodopsin I as a two-photon-driven proton pump.
Haupts U, Haupts C, Oesterhelt D Proc Natl Acad Sci U S A. 1995; 92(9):3834-8.
PMID: 11607531 PMC: 42056. DOI: 10.1073/pnas.92.9.3834.