| Autor: |
Balashov, SP, Imasheva, ES, Dioumaev, AK, Wang, JM, Jung, KH, Lanyi, JK |
| Jazyk: |
angličtina |
| Rok vydání: |
2014 |
| Zdroj: |
Balashov, SP; Imasheva, ES; Dioumaev, AK; Wang, JM; Jung, KH; & Lanyi, JK. (2014). Light-driven Na+pump from Gillisia limnaea: A high-affinity Na+binding site is formed transiently in the photocycle. Biochemistry, 53(48), 7549-7561. doi: 10.1021/bi501064n. UC Irvine: Retrieved from: http://www.escholarship.org/uc/item/6tv553rz |
| Popis: |
© 2014 American Chemical Society. 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. 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. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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