التفاصيل البيبلوغرافية
| العنوان: |
Aspartate—Histidine Interaction in the Retinal Schiff Base Counterion of the Light-Driven Proton Pump of Exiguobacterium sibiricum. |
| المؤلفون: |
Balashov, S. P.1 balashov@uci.edu, Petrovskaya, L. E.2 jklanyi@uci.edu, Lukashev, E. P.3, Imasheva, E. S.1, Dioumaev, A. K.1, Wang, J. M.1, Sychev, S. V.2, Dolgikh, D. A.2,3, Rubin, A. B.3, Kirpichnikov, M. P.2,3, Lanyi, J. K.1 lpetr65@yahoo.com |
| المصدر: |
Biochemistry. 7/24/2012, Vol. 51 Issue 29, p5748-5762. 15p. |
| مصطلحات موضوعية: |
*PROTON pump inhibitors, *PROTEORHODOPSIN, *HYDROGEN bonding, *ESCHERICHIA coli, *ASPARTIC acid |
| مستخلص: |
One of the distinctive features of eubacterial retinal-based proton pumps, proteorhodopsins, xanthorhodopsin, and others, is hydrogen bonding of the key aspartate residue, the counterion to the retinal Schiff base, to a histidine. We describe properties of the recently found eubacteriwn proton pump from Exiguobacterluns sibiricum (named ESR) expressed in Escherichia coil, WT especially features that depend on Asp-His interaction, the protonation state of the key aspartate, Asp85, and its ability to accept a proton from the Schiff base during the photocycle. Proton pumping by liposomes and E. coli cells containing ESR occurs in abroad pH range above pH 4.5. Large light-induced pH changes indicate that ESR is a potent proton pump. Replacement of His57 with methionine or asparagine strongly affects the pH-dependent properties of ESR. In the H57M mutant, a dramatic decrease in the quantum yield of chromophore fluorescence emission and a 45 nm blue shift of the absorption maximum with an increase in the pH from 5 to 8 indicate deprotonation of the counterion with a pKa of 6.3, which is also the pKa at which the M intermediate is observed in the photocycle of the protein solubilized in detergent [dodecyl maltoside (DDM)). This is in contrast with the case for the wild.type protein, for which the same experiments show that the major fraction of Asp85 is deprotonated at pH >3 and that it protonates only at low pH, with a pKa of 2.3. The M intermediate in the wild-type photocyde accumulates only at high pH, with an apparent pKa of 9, via deprotonation of a residue interacting with Asp85, presumably His57. In liposomes reconstituted with ESR, the pKa values for M formation and spectral shifts are 2-3 pH units lower than in DDM. The distinctively different pH dependencies of the protonation of Asp85 and the accumulation of the M intermediate in the wild-type protein versus the H57M mutant indicate that there is strong Asp-His interaction, which substantially lowers the pKa of Asp85 by stabilizing its deprotonated state. [ABSTRACT FROM AUTHOR] |
| قاعدة البيانات: |
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