TY - JOUR
T1 - Correlation of the O-intermediate rate with the pKa of Asp-75 in the dark, the counterion of the Schiff base of pharaonis phoborhodopsin (sensory rhodopsin II)
AU - Iwamoto, Masayuki
AU - Sudo, Yuki
AU - Shimono, Kazumi
AU - Araiso, Tsunehisa
AU - Kamo, Naoki
N1 - Funding Information:
This work was supported by Research Fellowships from the Japan Society for the Promotion of Science for Young Scientists to M.I.
PY - 2005/2
Y1 - 2005/2
N2 - Pharaonis phoborhodopsin (ppR), also called pharaonis sensory rhodopsin II, NpSRII, is a photoreceptor of negative phototaxis in Natronomonas (Natronobacterium) pharaonis. The photocycle rate of ppR is slow compared to that of bacteriorhodopsin, despite the similarity in their x-ray structures. The decreased rate of the photocycle of ppR is a result of the longer lifetime of later photo-intermediates such as M- (ppRM) and O-intermediates (ppRO). In this study, mutants were prepared in which mutated residues were located on the extracellular surface (P182, P183, and V194) and near the Schiff base (T204) including single, triple (P182S/P183E/V194T), and quadruple mutants. The decay of ppRO of the triple mutant was accelerated ∼20-times from 690 ms for the wild-type to 36 ms. Additional mutation resulting in a triple mutant at the 204th position such as T204C or T204S further decreased the decay half-time to 6.6 or 8 ms, almost equal to that of bacteriorhodopsin. The decay half-times of the ppRO of mutants (11 species) and those of the wild-type were well-correlated with the pK a value of Asp-75 in the dark for the respective mutants as spectroscopically estimated, although there are some exceptions. The implications of these observations are discussed in detail.
AB - Pharaonis phoborhodopsin (ppR), also called pharaonis sensory rhodopsin II, NpSRII, is a photoreceptor of negative phototaxis in Natronomonas (Natronobacterium) pharaonis. The photocycle rate of ppR is slow compared to that of bacteriorhodopsin, despite the similarity in their x-ray structures. The decreased rate of the photocycle of ppR is a result of the longer lifetime of later photo-intermediates such as M- (ppRM) and O-intermediates (ppRO). In this study, mutants were prepared in which mutated residues were located on the extracellular surface (P182, P183, and V194) and near the Schiff base (T204) including single, triple (P182S/P183E/V194T), and quadruple mutants. The decay of ppRO of the triple mutant was accelerated ∼20-times from 690 ms for the wild-type to 36 ms. Additional mutation resulting in a triple mutant at the 204th position such as T204C or T204S further decreased the decay half-time to 6.6 or 8 ms, almost equal to that of bacteriorhodopsin. The decay half-times of the ppRO of mutants (11 species) and those of the wild-type were well-correlated with the pK a value of Asp-75 in the dark for the respective mutants as spectroscopically estimated, although there are some exceptions. The implications of these observations are discussed in detail.
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U2 - 10.1529/biophysj.104.045583
DO - 10.1529/biophysj.104.045583
M3 - Article
C2 - 15533927
AN - SCOPUS:21244436327
VL - 88
SP - 1215
EP - 1223
JO - Biophysical Journal
JF - Biophysical Journal
SN - 0006-3495
IS - 2
ER -