Detection of bacteriorhodopsin trimeric rotation at thermal phase transitions of purple membrane in suspension

• Published in: Biophysical chemistry Vol. 300; p. 107074
• Main Author: Mostafa, Hamdy I.A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.09.2023
• Subjects: Bacteriorhodopsin; Phase transition; Purple membrane; Rotational diffusion; Bacteriorhodopsin; Rotational diffusion; Purple membrane; Phase transition
• ISSN: 0301-4622; 1873-4200
• DOI: 10.1016/j.bpc.2023.107074

Bacteriorhodopsin (bR) of purple membrane (PM) is a retinal protein that forms aggregates in the form of trimers constituting, together with archaeal lipids, the crystalline structure of PM. The rotary motion of bR inside PM may be pertinent in understanding the essence of the crystalline lattice. An attempt has been made to determine the rotation of bR trimers which has been found to be detected solely at thermal phase transitions of PM, namely lipid, crystalline lattice and protein melting phase transitions. The temperature dependences of dielectric versus electronic absorption spectra of bR have been determined. The results suggest that the rotation of bR trimers, together with concomitant bending of PM, are most likely brought by structural changes in bR which might be driven by retinal isomerization and mediated by lipid. The rupturing of the lipid-protein contact might consequently lead to rotation of trimers associated with bending, curling or vesicle formation of PM. So the retinal reorientation may underlie the concomitant rotation of trimers. Most importantly, rotation of trimers might play a role, in terms of the essence of the crystalline lattice, in the functional activity of bR and may serve physiological relevance. [Display omitted] •The bR trimers reorientation inside PM occurs solely at thermal phase transitions of PM implying disordering in bR crystal lattice at such thermal transitions.•It is the retinal reorientation that underlies the rotation of bR trimers within PM.•Rotation of bR trimers inside PM, in terms of the essence of its crystalline lattice, might play a role in the functional activity of bR and may serve physiological relevance.•Correlation of the dielectric function to conformational changes occurring in bR.•Direct proportion of the retinal absorption to the dielectric function within the protein matrix of bR.