期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 114, 期 51, 页码 E10909-E10918出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1707993114
关键词
time-resolved infrared spectroscopy; proton release; proton uptake; protonated water clusters; continuum band
资金
- Spanish Ministry of Economy, Industry and Competitiveness [BFU2016-768050-P]
- Ramon y Cajal Fellowship [RYC-2013-13114]
- German Research Foundation [SFB-1078]
Infrared spectroscopy has been used in the past to probe the dynamics of internal proton transfer reactions taking place during the functional mechanism of proteins but has remained mostly silent to protonation changes in the aqueous medium. Here, by selectively monitoring vibrational changes of buffer molecules with a temporal resolution of 6 mu s, we have traced proton release and uptake events in the light-driven proton-pump bacteriorhodopsin and correlate these to other molecular processes within the protein. We demonstrate that two distinct chemical entities contribute to the temporal evolution and spectral shape of the continuum band, an unusually broad band extending from 2,300 to well below 1,700 cm(-1). The first contribution corresponds to deprotonation of the proton release complex (PRC), a complex in the extracellular domain of bacteriorhodopsin where an excess proton is shared by a cluster of internal water molecules and/or ionic E194/E204 carboxylic groups. We assign the second component of the continuum band to the proton uptake complex, a cluster with an excess proton reminiscent to the PRC but located in the cytoplasmic domain and possibly stabilized by D38. Our findings refine the current interpretation of the continuum band and call for a reevaluation of the last proton transfer steps in bacteriorhodopsin.
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