@article {1163,
	title = {Partial dehydration of the retinal binding pocket and proof for photochemical deprotonation of the retinal Schiff base in bicelle bacteriorhodopsin crystals},
	journal = {Photochemistry and Photobiology},
	volume = {81},
	number = {6},
	year = {2005},
	note = {Sanii, LS El-Sayed, MA},
	month = {Nov-Dec},
	pages = {1356-1360},
	abstract = {In bicelle bacteriorhodopsin (bcbR) crystals, the protein has a different structure from both native bacteriorhodopsin (bR) and in-cubo bR (cbR) crystals. Recently, we studied the ability of bcbR crystals to undergo the photocycle upon laser excitation, characterized by the appearance of the M intermediate by single crystal resonance Raman spectroscopy. Calculation of the M lifetime by flash photolysis experiments demonstrated that in our bchR crystals, the M rise time is much faster than in the native or cbR crystals, with a decay time that is much slower than these other two forms. Although it is now known that the bcbR crystals are capable of photochemical deprotonation, it is not known whether photochemical deprotonation is the only way to create the deprotonated Schiff base in the bcbR crystals. We measured both the visible and Raman spectra of crystals dried under ambient lighting and dried in the dark in order to determine whether the retinal Schiff base is able to thermally deprotonate in the dark. In addition, changes in the visible spectrum of single bcbR crystals under varying degrees of hydration and light exposure were examined to better understand the retinal binding environment.},
	isbn = {0031-8655},
	doi = {10.1562/2005-03-09-ra-458},
	author = {Sanii, L. S. and El-Sayed, Mostafa A}
}
@article {1162,
	title = {The protonation-deprotonation kinetics of the protonated Schiff base in bicelle bacteriorhodopsin crystals},
	journal = {Biophysical Journal},
	volume = {89},
	number = {1},
	year = {2005},
	note = {Sanii, LS Schill, AW Moran, CE El-Sayed, MA},
	month = {Jul},
	pages = {444-451},
	abstract = {In the recently published x-ray crystal structure of the "bicelle" bacteriorhodopsin (bbR) crystal, the protein has quite a different structure from the native and the in cubo bacteriorhodopsin (cbR) crystal. Instead of packing in parallel trimers as do the native membrane and the cbR crystals, in the bbR crystal the protein packs as antiparallel monomers. To date, no functional studies have been performed, to our knowledge, to investigate if the photocycle is observed in this novel protein packing structure. In this study, both Raman and time-resolved transient absorption spectroscopy are used to both confirm the presence of the photocycle and investigate the deprotonation-reprotonation kinetics of the Schiff base proton in the bbR crystal. The observed rates of deprotonation and reprotonation processes of its Schiff base have been compared to those observed for native bR under the same conditions. Unlike the previously observed similarity of the rates of these processes for cbR crystals and those for native bacteriorhodopsin (bR), in bbR crystals the rate of deprotonation has increased by 300\%, and the rate of reprotonation has decreased by nearly 700\%. These results are discussed in light of the changes observed when native bR is delipidated or monomerized by detergents. Both the change of the hydrophobicity of the environment around the protonated Schiff base and Asp(85) and Asp(96) (which could change the pK(a) values of proton donor-acceptor pairs) and the water structure in the bbR crystal are offered as possible explanations for the different observations.},
	isbn = {0006-3495},
	doi = {10.1529/biophysj.105.059675},
	author = {Sanii, L. S. and Schill, A. W. and Moran, C. E. and El-Sayed, Mostafa A}
}
