title: Consequences of counterion mutation in sensory rhodopsin II of Natronobacterium pharaonis for photoreaction and receptor activation: an FTIR study.
abstract: In many retinal proteins the proton transfer from the Schiff base to the counterion represents a functionally important step of the photoreaction. In the signaling state of sensory rhodopsin II from Natronobacterium pharaonis this transfer has already occurred, but in the counterion mutant Asp75Asn it is blocked during all steps of the photocycle. Therefore, the study of the molecular changes during the photoreaction of this mutant should provide a deeper understanding of the activation mechanism, and for this, we have applied time-resolved step-scan FTIR spectroscopy. The photoreaction is drastically altered; only red-shifted intermediates are formed with a chromophore strongly twisted around the 14-15 single bond. In addition, the photocycle is shortened by 2 orders of magnitude. Nevertheless, a transition involving only protein changes similar to that of the wild type is observed, which has been correlated with the formation of the signaling state. However, whereas in the wild type this transition occurs in the millisecond range, it is shortened to 200 micros in the mutant. The results are discussed with respect to the altered electrostatic interactions, role of proton transfer, the published 3D structure, and physiological activity.
authors.affiliation: Sektion Biophysik, Institut für Molekulare Medizin und Zellforschung, Albert-Ludwigs-Universität, Hermann-Herderstrasse 9, 79104 Freiburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Hein
authors.forename: Ionela
authors.initials: I
authors.lastname: Radu
authors.forename: Johann P
authors.initials: JP
authors.lastname: Klare
authors.forename: Martin
authors.initials: M
authors.lastname: Engelhard
authors.forename: Friedrich
authors.initials: F
authors.lastname: Siebert
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D001216:Asparagine / Q000235:genetics; D001224:Aspartic Acid / Q000235:genetics; D002338:Carotenoids / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D005615:Freezing; D025602:Halorhodopsins; D006863:Hydrogen-Ion Concentration; D019633:Natronobacterium / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D010777:Photochemistry / Q000379:methods; D017354:Point Mutation; D011522:Protons; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D012545:Schiff Bases / Q000737:chemistry; D025603:Sensory Rhodopsins; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
chemical_list: D019843:Archaeal Proteins; D025602:Halorhodopsins; D011522:Protons; D043562:Receptors, G-Protein-Coupled; D012545:Schiff Bases; D025603:Sensory Rhodopsins; C061508:sensory rhodopsin II protein, archaeal; D001224:Aspartic Acid; D002338:Carotenoids; D001216:Asparagine