Factors that differentiate the H-bond strengths of water near the Schiff bases in bacteriorhodopsin and Anabaena sensory rhodopsin.
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Abstract
Bacteriorhodopsin (BR) functions as a light-driven proton pump, whereas Anabaena sensory rhodopsin (ASR) is believed to function as a photosensor despite the high similarity in their protein sequences. In Fourier transform infrared (FTIR) spectroscopic studies, the lowest O-D stretch for D(2)O was observed at ∼2200 cm(-1) in BR but was significantly higher in ASR (>2500 cm(-1)), which was previously attributed to a water molecule near the Schiff base (W402) that is H-bonded to Asp-85 in BR and Asp-75 in ASR. We investigated the factors that differentiate the lowest O-D stretches of W402 in BR and ASR. Quantum mechanical/molecular mechanical calculations reproduced the H-bond geometries of the crystal structures, and the calculated O-D stretching frequencies were corroborated by the FTIR band assignments. The potential energy profiles indicate that the smaller O-D stretching frequency in BR originates from the significantly higher pK(a)(Asp-85) in BR relative to the pK(a)(Asp-75) in ASR, which were calculated to be 1.5 and -5.1, respectively. The difference is mostly due to the influences of Ala-53, Arg-82, Glu-194-Glu-204, and Asp-212 on pK(a)(Asp-85) in BR and the corresponding residues Ser-47, Arg-72, Ser-188-Asp-198, and Pro-206 on pK(a)(Asp-75) in ASR. Because these residues participate in proton transfer pathways in BR but not in ASR, the presence of a strongly H-bonded water molecule near the Schiff base ultimately results from the proton-pumping activity in BR.
Journal
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- The Journal of biological chemistry
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The Journal of biological chemistry 287 (41), 34009-34018, 2012-10-05
American Society for Biochemistry and Molecular Biology
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Keywords
Details 詳細情報について
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- CRID
- 1050564285712658944
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- NII Article ID
- 120005241372
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- NII Book ID
- AA00251083
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- ISSN
- 00219258
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- HANDLE
- 2433/169708
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- Text Lang
- en
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- Article Type
- journal article
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- Data Source
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- IRDB
- CiNii Articles