Water-Mediated Proton Transfer in Proteins: An FTIR Study of Bacteriorhodopsin

• Published in: Journal of the American Chemical Society Vol. 117; no. 7; pp. 2118 - 2119
• Main Authors: Kandori, Hideki, Yamazaki, Yoichi, Sasaki, Jun, Needleman, Richard, Lanyi, Janos K, Maeda, Akio
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.02.1995
• Subjects: 400102 > Chemical & Spectral Procedures; 550700 > Microbiology; ABSORPTION SPECTROSCOPY; BACTERIA; BASIC BIOLOGICAL SCIENCES; CHARGED-PARTICLE TRANSPORT; CHEMICAL BONDS; FOURIER TRANSFORM SPECTROMETERS; INFRARED SPECTRA; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MEASURING INSTRUMENTS; MICROORGANISMS; ORGANIC COMPOUNDS; PIGMENTS; PROTEINS; PROTON TRANSPORT; RADIATION TRANSPORT; RHODOPSIN; SPECTRA; SPECTROMETERS; SPECTROSCOPY 400201 > Chemical & Physicochemical Properties
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00112a036

Fourier transform infrared (FTIR) spectroscopy was used to investigate structural changes of water that precede the initial proton transfer reaction in bacteriorhodopsin. The Asp212 arrow right Asn (D212N) protein under alkaline conditions where M is not formed (i.e., there is no proton transfer) was compared with the wild-type and Asp85 arrow right Asn (D85N) proteins at 170 K for the O-H stretching mode of water. The observed increase in the H-bonding strength of water is very small in D212N and absent in D85N, in contrast to the wild-type bacteriorhodopsin at the intermediate stage before proton transfer (L intermediate). On the basis of these results, we conclude that, besides H-bonding of a water molecule between the Schiff base and Asp85, the formation of H-bonding with Asp212 of the originally unbound O-H is required for the proton transfer.