TY - JOUR
T1 - The lifetimes of pharaonis phoborhodopsin signaling states depend on the rates of proton transfers-Effects of hydrostatic pressure and stopped flow experiments
AU - Kikukawa, Takashi
AU - Saha, Chabita K.
AU - Balashov, Sergei P.
AU - Imasheva, Eleonora S.
AU - Zaslavsky, Dmitry
AU - Gennis, Robert B.
AU - Abe, Takayuki
AU - Kamo, Naoki
PY - 2008/7
Y1 - 2008/7
N2 - Pharaonis phoborhodopsin (ppR), a negative phototaxis receptor of Natronomonas pharaonis, undergoes photocycle similar to the light-driven proton pump bacteriorhodopsin (BR), but the turnover rate is much slower due to much longer lifetimes of the M and O intermediates. The M decay was shown to become as fast as it is in BR in the L40T / F86D mutant. We examined the effects of hydrostatic pressure on the decay of these intermediates. For BR, pressure decelerated M decay but slightly affected O decay. In contrast, with ppR and with its L40T / F86D mutant, pressure slightly affected M decay but accelerated O decay. Clearly, the pressure-dependent factors for Mand O decay are different in BR and ppR. In order to examine the deprotonation of Asp75 in unphotolyzed ppR we performed stopped flow experiments. The pH jump-induced deprotonation of Asp75 occurred with 60 ms, which is at least 20 times slower than deprotonation of the equivalent Asp85 in BR and about 10-fold faster than the O decay of ppR. These data suggest that proton transfer is slowed not only in the cytoplasmic channel but also in the extracellular channel of ppR and that the lightinduced structural changes in the O intermediate of ppR additionally decrease this rate.
AB - Pharaonis phoborhodopsin (ppR), a negative phototaxis receptor of Natronomonas pharaonis, undergoes photocycle similar to the light-driven proton pump bacteriorhodopsin (BR), but the turnover rate is much slower due to much longer lifetimes of the M and O intermediates. The M decay was shown to become as fast as it is in BR in the L40T / F86D mutant. We examined the effects of hydrostatic pressure on the decay of these intermediates. For BR, pressure decelerated M decay but slightly affected O decay. In contrast, with ppR and with its L40T / F86D mutant, pressure slightly affected M decay but accelerated O decay. Clearly, the pressure-dependent factors for Mand O decay are different in BR and ppR. In order to examine the deprotonation of Asp75 in unphotolyzed ppR we performed stopped flow experiments. The pH jump-induced deprotonation of Asp75 occurred with 60 ms, which is at least 20 times slower than deprotonation of the equivalent Asp85 in BR and about 10-fold faster than the O decay of ppR. These data suggest that proton transfer is slowed not only in the cytoplasmic channel but also in the extracellular channel of ppR and that the lightinduced structural changes in the O intermediate of ppR additionally decrease this rate.
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U2 - 10.1111/j.1751-1097.2008.00318.x
DO - 10.1111/j.1751-1097.2008.00318.x
M3 - Article
C2 - 18346087
AN - SCOPUS:52149113758
SN - 0031-8655
VL - 84
SP - 880
EP - 888
JO - Photochemistry and Photobiology
JF - Photochemistry and Photobiology
IS - 4
ER -