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Structural Transition of Bacteriorhodopsin Is Preceded by Deprotonation of Schiff Base: Microsecond Time-Resolved X-Ray Diffraction Study of Purple Membrane
The structural changes in the photoreaction cycle of bacteriorhodopsin, a light-driven proton pump, was investigated at a resolution of 7 Å by a time-resolved x-ray diffraction experiment utilizing synchrotron x rays from an undulator of SPring-8. The x-ray diffraction measurement system, used in co...
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| Main Authors: | , , , |
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| Formato: | Artigo |
| Idioma: | English |
| Publicado em: |
The Biophysical Society
2005
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| Assuntos: | |
| Acesso em linha: | https://ncbi.nlm.nih.gov/pmc/articles/PMC1305020/ https://ncbi.nlm.nih.gov/pubmed/15516520 https://ncbi.nlm.nih.govhttp://dx.doi.org/10.1529/biophysj.104.051748 |
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| Resumo: | The structural changes in the photoreaction cycle of bacteriorhodopsin, a light-driven proton pump, was investigated at a resolution of 7 Å by a time-resolved x-ray diffraction experiment utilizing synchrotron x rays from an undulator of SPring-8. The x-ray diffraction measurement system, used in coupling with a pulsed YAG laser, enabled us to record a diffraction pattern from purple membrane film at a time-resolution of 6 μs over the time domain of 5 μs to 500 ms. In the time domain, the functionally most important M-intermediate appears. A series of time-resolved x-ray diffraction data after photo-excitation showed clear intensity changes caused by the conformational changes of helix G in the M-intermediate. The population of the reaction intermediate was prominently observed at ∼5 ms after a photo-stimulus. In contrast, absorption measurement indicated the deprotonation of the Schiff base predominantly occurred at ∼300 μs after a photo-stimulus. These results showed that the conformational changes characterizing structurally the M-intermediate predominantly occur at a later stage of the deprotonation of the Schiff base. Thus, the M-intermediate can be divided into two metastable stages with different physical characteristics. |
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