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Tryptophan 171 in Pharaonis Phoborhodopsin (Sensory Rhodopsin II) Interacts with the Chromophore Retinal and its Substitution with Alanine or Threonine Slowed Down the Decay of M‐ and O‐intermediate †
Author(s) -
Iwasa Tatsuo,
Abe Eisuke,
Yakura Yuki,
Yoshida Hideaki,
Kamo Naoki
Publication year - 2007
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/2006-06-15-ra-928
Subject(s) - bacteriorhodopsin , chromophore , tryptophan , retinal , rhodopsin , chemistry , threonine , hydrogen bond , halobacteriaceae , photochemistry , alanine , stereochemistry , biophysics , biochemistry , serine , biology , molecule , amino acid , halobacterium salinarum , phosphorylation , organic chemistry , membrane
Pharaonis phoborhodopsin ( p pR), also called pharaonis sensory rhodopsin II, NpSRII, is a photoreceptor for the photophobic response of Natronomonas pharaonis . Tryptophan 182 (W182) of bacteriorhodopsin (bR) is near the chromophore retinal and has been suggested to interact with retinal during the photoreaction and also to be involved in the hydrogen‐bonding network around the retinal. W182 of bR is conserved in p pR as tryptophan 171 (W171). To elucidate whether W171 of p pR interacts with retinal during the photoreaction and/or is involved in the hydrogen‐bonding network as in bR, we formed W171‐substituted mutants of p pR, W171A and W171T. Our low‐temperature spectroscopic study has revealed that the substitution of W171 to Ala or Thr resulted in the stabilization of M‐ and O‐intermediates. The stability of M and absorption spectral changes during the M‐decay were different depending on the substituted residue. These findings suggest that W171 in p pR interacts with retinal and the degree of the interaction depends on the substituted residues, which might be rate determining in the M‐decay. In addition, the involvement of W171 in the hydrogen‐bonding network is suggested by the O‐decay. We also found that glycerol slowed the decay of M and not of O.