I. Rousso et al., EVIDENCE FOR A CONTROLLING ROLE OF WATER IN PRODUCING THE NATIVE BACTERIORHODOPSIN STRUCTURE, Biophysical journal, 73(4), 1997, pp. 2081-2089
The experiments reported in this paper, based on reconstitution of bac
teriorhodopsin (bR) from apomembrane at varying environmental conditio
ns, demonstrate that the presence of water is a controlling factor in
generating a native wild-type bR conformation. If water is lacking dur
ing this reconstitution process, then a non-native bR structure is for
med that exhibits altered M formation and decay kinetics, as well as d
ifferent behavior following extensive dehydration, It is shown that mu
tants affecting the ability of bR to form appropriate structures of wa
ter in specific protein cavities also affect the ability to generate a
native bR conformation, The results suggest that aspartic acid 96 pla
ys a major role in anchoring the appropriate water structure conformat
ion associated with bR. It is also demonstrated that the glutamic acid
204 residue is pivotal in controlling the protein/water affinity. Thi
s water affinity can be further controlled by modifying the charge env
ironment of the protein with altered pH. These data, based on kinetic
absorption spectroscopy and Fourier transform infrared spectroscopy, h
ighlight the central role of water in this protein.