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Title: Light-driven Na + pump from Gillisia limnaea: A high-affinity Na + binding site is formed transiently in the photocycle

A group of microbial retinal proteins most closely related to the proton pump xanthorhodopsin has a novel sequence motif and a novel function. Instead of, or in addition to, proton transport, they perform light-driven sodium ion transport, as reported for one representative of this group (KR2) from Krokinobacter. In this paper, we examine a similar protein, GLR from Gillisia limnaea, expressed in Escherichia coli, which shares some properties with KR2 but transports only Na +. The absorption spectrum of GLR is insensitive to Na + at concentrations of ≤3 M. However, very low concentrations of Na + cause profound differences in the decay and rise time of photocycle intermediates, consistent with a switch from a “Na +-independent” to a “Na +-dependent” photocycle (or photocycle branch) at ~60 μM Na +. The rates of photocycle steps in the latter, but not the former, are linearly dependent on Na + concentration. This suggests that a high-affinity Na + binding site is created transiently after photoexcitation, and entry of Na + from the bulk to this site redirects the course of events in the remainder of the cycle. A greater concentration of Na + is needed for switching the reaction path at lowermore » pH. The data suggest therefore competition between H + and Na + to determine the two alternative pathways. The idea that a Na + binding site can be created at the Schiff base counterion is supported by the finding that upon perturbation of this region in the D251E mutant, Na + binds without photoexcitation. Furthermore, binding of Na+ to the mutant shifts the chromophore maximum to the red like that of H +, which occurs in the photocycle of the wild type.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [1]
  1. Univ. of California, Irvine, CA (United States)
  2. Sogang Univ., Seoul (Korea)
Publication Date:
Grant/Contract Number:
FG03-86ER13525; DEFG03-86ER13525
Type:
Published Article
Journal Name:
Biochemistry
Additional Journal Information:
Journal Volume: 53; Journal Issue: 48; Journal ID: ISSN 0006-2960
Publisher:
American Chemical Society (ACS)
Research Org:
Univ. of California, Irvine, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES; 60 APPLIED LIFE SCIENCES
OSTI Identifier:
1165228
Alternate Identifier(s):
OSTI ID: 1345588

Balashov, Sergei P., Imasheva, Eleonora S., Dioumaev, Andrei K., Wang, Jennifer M., Jung, Kwang -Hwan, and Lanyi, Janos K.. Light-driven Na+ pump from Gillisia limnaea: A high-affinity Na+ binding site is formed transiently in the photocycle. United States: N. p., Web. doi:10.1021/bi501064n.
Balashov, Sergei P., Imasheva, Eleonora S., Dioumaev, Andrei K., Wang, Jennifer M., Jung, Kwang -Hwan, & Lanyi, Janos K.. Light-driven Na+ pump from Gillisia limnaea: A high-affinity Na+ binding site is formed transiently in the photocycle. United States. doi:10.1021/bi501064n.
Balashov, Sergei P., Imasheva, Eleonora S., Dioumaev, Andrei K., Wang, Jennifer M., Jung, Kwang -Hwan, and Lanyi, Janos K.. 2014. "Light-driven Na+ pump from Gillisia limnaea: A high-affinity Na+ binding site is formed transiently in the photocycle". United States. doi:10.1021/bi501064n.
@article{osti_1165228,
title = {Light-driven Na+ pump from Gillisia limnaea: A high-affinity Na+ binding site is formed transiently in the photocycle},
author = {Balashov, Sergei P. and Imasheva, Eleonora S. and Dioumaev, Andrei K. and Wang, Jennifer M. and Jung, Kwang -Hwan and Lanyi, Janos K.},
abstractNote = {A group of microbial retinal proteins most closely related to the proton pump xanthorhodopsin has a novel sequence motif and a novel function. Instead of, or in addition to, proton transport, they perform light-driven sodium ion transport, as reported for one representative of this group (KR2) from Krokinobacter. In this paper, we examine a similar protein, GLR from Gillisia limnaea, expressed in Escherichia coli, which shares some properties with KR2 but transports only Na+. The absorption spectrum of GLR is insensitive to Na+ at concentrations of ≤3 M. However, very low concentrations of Na+ cause profound differences in the decay and rise time of photocycle intermediates, consistent with a switch from a “Na+-independent” to a “Na+-dependent” photocycle (or photocycle branch) at ~60 μM Na+. The rates of photocycle steps in the latter, but not the former, are linearly dependent on Na+ concentration. This suggests that a high-affinity Na+ binding site is created transiently after photoexcitation, and entry of Na+ from the bulk to this site redirects the course of events in the remainder of the cycle. A greater concentration of Na+ is needed for switching the reaction path at lower pH. The data suggest therefore competition between H+ and Na+ to determine the two alternative pathways. The idea that a Na+ binding site can be created at the Schiff base counterion is supported by the finding that upon perturbation of this region in the D251E mutant, Na+ binds without photoexcitation. Furthermore, binding of Na+ to the mutant shifts the chromophore maximum to the red like that of H+, which occurs in the photocycle of the wild type.},
doi = {10.1021/bi501064n},
journal = {Biochemistry},
number = 48,
volume = 53,
place = {United States},
year = {2014},
month = {11}
}