Semiconductor quantum dots affect fluidity of purple membrane from Halobacterium salinarum through disruption of bacteriorhodopsin trimer organization

International audience; Bacteriorhodopsin (bR) is a unique protein of purple membranes (PMs) of the bacterium Halobacterium salinarum. Tight trimers of this integral photochromic protein form a highly ordered 2D hexagonal crystalline lattice within the PMs. Due to strong excitonic interactions between the bR chromophores (retinals) in the protein trimers, PMs exhibit a strong circular dichroism (CD) activity in the region of the retinal absorption band, which allows monitoring the regularity and stability of the bR trimer organization within the membrane. In this study, the effects of semiconductor quantum dots (QDs) on the bR intramembrane organization and the time course of bR monomerization caused by detergents have been analyzed. The results show that the interaction with QDs does not influence the bR structural organization but considerably accelerates the monomerization of the protein by detergents. These data have been confirmed by the results of atomic force microscopy (AFM) followed by Fourier transform analysis, which have shown that interactions with QDs cause an eightfold acceleration of bR monomerization with Triton. The data show that interactions of nanoparticles with biological membranes may modulate the membrane fluidity and the structural organization and function of integral proteins embedded in these membranes.