@article {1192,
	title = {Refolding of thermally denatured bacteriorhodopsin in purple membrane},
	journal = {Journal of Physical Chemistry B},
	volume = {106},
	number = {3},
	year = {2002},
	note = {Wang, JP Heyes, CD El-Sayed, MA},
	month = {Jan},
	pages = {723-729},
	abstract = {The change in protein conformational structure and retinal chromophore binding state have been examined by using in situ UV-vis, FTIR, and CD spectroscopies during the thermal denaturation and refolding processes in bacteriorhodopsin (bR) of purple membrane (PM), in its native trimeric and in Triton X-100 solubilized monomeric form. For the trimeric bR, it is found that heating bR through its premelting transition (T > 78 degreesC, T-m{\textquoteright}) does not cause any permanent damage in the protein secondary structure, and a reversible refolding occurs when it cools back to room temperature. For the monomeric bR, it is found that it is less thermally stable than the trimer. There is a significant change in its protein secondary structure and a complete dissociation of retinal occurs irreversibly at a temperature as low as 66 degreesC. In addition, it is found that heating the trimeric bR through its main molten state (T > 96 degreesC, T-m) changes the protein secondary structure so that bR does not refold fully into its original secondary structure. Upon cooling back to room temperature, about 90\% of the bound retinal in native bR recovers after being heated through its premelting transition, whereas only about 12\% of bound retinal recovers if bR is heated above its main melting temperature. It is also found that refolded bR molecules with their retinal chromophore rebound have a photocycle and are capable of pumping protons. Our results also suggest that from its molten state, protein secondary structure refolding precedes retinal rebinding to the Schiff base.},
	isbn = {1520-6106},
	doi = {10.1021/jp013131a},
	author = {Wang, Jianping and Heyes, C D and El-Sayed, Mostafa A}
}
@article {1203,
	title = {The role of the native lipids and lattice structure in bacteriorhodopsin protein conformation and stability as studied by temperature-dependent Fourier transform-infrared spectroscopy},
	journal = {Journal of Biological Chemistry},
	volume = {277},
	number = {33},
	year = {2002},
	note = {Heyes, CD El-Sayed, MA},
	month = {Aug},
	pages = {29437-29443},
	abstract = {We report the effect of partial delipidation and monomerization on the protein conformational changes of bacteriorhodopsin (bR) as a function of temperature. Removal of up to 75\% of the lipids is known to have the lattice structure of the purple membrane, albeit as a smaller unit cell, whereas treatment by Triton monomerizes bR into micelles. The effects of these modifications on the protein secondary structure is analyzed by monitoring the protein amide I and amide II bands in the Fourier transform-infrared (FT-IR) spectra. It is found that removal of the first 75\% of the lipids has only a slight effect on the secondary structure at physiological temperature, whereas monomerizing bR into micelles alters the secondary structure considerably. Upon heating, the bR monomer is found to have a very low thermal stability compared with the native bR with its melting point reduced from 97 to 65 degreesC, and the premelting transition in which the protein changes conformation in native bR at 80 degreesC could not be observed. Also, the N-H to N-D exchange of the amide II band is effectively complete at room temperature, suggesting that there are no hydrophobic regions that are protected from the aqueous medium, possibly explaining the low thermal stability of the monomer. On the other hand, 75\% delipidated bR has its melting temperature close to that of the native bR and does have a pre-melting transition, although the pre-melting transition occurs at significantly higher temperature than that of the native bR (91 degreesC compared with 80 degreesC) and is still reversible. Furthermore, we have also observed that the reversibility of this pre-melting transition of both native and partially delipidated bR is time-dependent and becomes irreversible upon holding at 91 degreesC between 10 and 30 min. These results are discussed in terms of the lipid and lattice contribution to the protein thermal stability of native bR.},
	isbn = {0021-9258},
	doi = {10.1074/jbc.M203435200},
	author = {Heyes, C D and El-Sayed, Mostafa A}
}
