Abstract
The light-driven proton pump bacteriorhodopsin (bR) undergoes a bleaching reaction with hydroxylamine in the dark, which is markedly catalyzed by light. The reaction involves cleavage of the (protonated) Schiff base bond, which links the retinyl chromophore to the protein. The catalytic light effect is currently attributed to the conformational changes associated with the photocycle of all-trans bR, which is responsible for its proton pump mechanism and is initiated by the all-trans --> 13-cis isomerization. This hypothesis is now being tested in a series of experiments, at various temperatures, using three artificial bR molecules in which the essential C13==C14 bond is locked by a rigid ring structure into an all-trans or 13-cis configuration. In all three cases we observe an enhancement of the reaction by light despite the fact that, because of locking of the C13==C14 bond, these molecules do not exhibit a photocycle, or any proton-pump activity. An analysis of the rate parameters excludes the possibility that the light-catalyzed reaction takes place during the approximately 20-ps excited state lifetimes of the locked pigments. It is concluded that the reaction is associated with a relatively long-lived (micros-ms) light-induced conformational change that is not reflected by changes in the optical spectrum of the retinyl chromophore. It is plausible that analogous changes (coupled to those of the photocycle) are also operative in the cases of native bR and visual pigments. These conclusions are discussed in view of the light-induced conformational changes recently detected in native and artificial bR with an atomic force sensor.
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Selected References
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- Bhattacharya S., Marti T., Otto H., Heyn M. P., Khorana H. G. A bacteriorhodopsin analog reconstituted with a nonisomerizable 13-trans retinal derivative displays light insensitivity. J Biol Chem. 1992 Apr 5;267(10):6757–6762. [PubMed] [Google Scholar]
- Bhattacharya S., Ridge K. D., Knox B. E., Khorana H. G. Light-stable rhodopsin. I. A rhodopsin analog reconstituted with a nonisomerizable 11-cis retinal derivative. J Biol Chem. 1992 Apr 5;267(10):6763–6769. [PubMed] [Google Scholar]
- Delaney J. K., Brack T. L., Atkinson G. H., Ottolenghi M., Steinberg G., Sheves M. Primary picosecond molecular events in the photoreaction of the BR5.12 artificial bacteriorhodopsin pigment. Proc Natl Acad Sci U S A. 1995 Mar 14;92(6):2101–2105. doi: 10.1073/pnas.92.6.2101. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kalisky O., Goldschmidt C. R., Ottolenghi M. On the photocycle and light adaptation of dark-adapted bacteriorhodopsin. Biophys J. 1977 Aug;19(2):185–189. doi: 10.1016/S0006-3495(77)85579-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Korenstein R., Hess B. Hydration effects on cis--trans isomerization of bacteriorhodopsin. FEBS Lett. 1977 Oct 1;82(1):7–11. doi: 10.1016/0014-5793(77)80874-0. [DOI] [PubMed] [Google Scholar]
- Oesterhelt D., Meentzen M., Schuhmann L. Reversible dissociation of the purple complex in bacteriorhodopsin and identification of 13-cis and all-trans-retinal as its chromophores. Eur J Biochem. 1973 Dec 17;40(2):453–463. doi: 10.1111/j.1432-1033.1973.tb03214.x. [DOI] [PubMed] [Google Scholar]
- Oesterhelt D., Schuhmann L., Gruber H. Light-dependent reaction of bacteriorhodopsin with hydroxylamine in cell suspensions of Halobacterium halobium: demonstration of an apo-membrane. FEBS Lett. 1974 Aug 30;44(3):257–261. doi: 10.1016/0014-5793(74)81152-x. [DOI] [PubMed] [Google Scholar]
- Oesterhelt D., Schuhmann L. Reconstitution of bacteriorhodopsin. FEBS Lett. 1974 Aug 30;44(3):262–265. doi: 10.1016/0014-5793(74)81153-1. [DOI] [PubMed] [Google Scholar]
- Oesterhelt D., Stoeckenius W. Isolation of the cell membrane of Halobacterium halobium and its fractionation into red and purple membrane. Methods Enzymol. 1974;31:667–678. doi: 10.1016/0076-6879(74)31072-5. [DOI] [PubMed] [Google Scholar]
- Rousso I., Friedman N., Sheves M., Ottolenghi M. pKa of the protonated Schiff base and aspartic 85 in the bacteriorhodopsin binding site is controlled by a specific geometry between the two residues. Biochemistry. 1995 Sep 19;34(37):12059–12065. doi: 10.1021/bi00037a049. [DOI] [PubMed] [Google Scholar]
- Rousso I., Khachatryan E., Gat Y., Brodsky I., Ottolenghi M., Sheves M., Lewis A. Microsecond atomic force sensing of protein conformational dynamics: implications for the primary light-induced events in bacteriorhodopsin. Proc Natl Acad Sci U S A. 1997 Jul 22;94(15):7937–7941. doi: 10.1073/pnas.94.15.7937. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Scherrer P., Mathew M. K., Sperling W., Stoeckenius W. Retinal isomer ratio in dark-adapted purple membrane and bacteriorhodopsin monomers. Biochemistry. 1989 Jan 24;28(2):829–834. doi: 10.1021/bi00428a063. [DOI] [PubMed] [Google Scholar]
- Subramaniam S., Marti T., Rösselet S. J., Rothschild K. J., Khorana H. G. The reaction of hydroxylamine with bacteriorhodopsin studied with mutants that have altered photocycles: selective reactivity of different photointermediates. Proc Natl Acad Sci U S A. 1991 Mar 15;88(6):2583–2587. doi: 10.1073/pnas.88.6.2583. [DOI] [PMC free article] [PubMed] [Google Scholar]