Spatial Organization of Bacteriorhodopsin in Model Membranes

Kahya, Nicoletta; Wiersma, Douwe A.; Poolman, Berend; Hoekstra, Dick

doi:10.1074/jbc.m202635200

Cited by 53 publications

(46 citation statements)

References 46 publications

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“…However, we did not observe any appreciable difference with the corresponding lifetimes measured for dark adapted membrane. Our observation contrasts with the results of Kahya et al who reported a decreased lateral mobility for photo-activated bR molecules due to formation of clusters comprising two or three trimers (Kahya et al, 2002). Their results, however, relied on fluorescence correlation spectroscopy and freeze-fracture electron microscopy of bR reconstituted in model membranes (giant unilamellar vesicles).…”

Section: Quantitative Analysis Of Intertrimer Interaction Energycontrasting

confidence: 99%

Dynamics of bacteriorhodopsin 2D crystal observed by high-speed atomic force microscopy

Yamashita

Voïtchovsky

Uchihashi

et al. 2009

Journal of Structural Biology

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We have used high-speed atomic force microscopy to study the dynamics of bacteriorhodopsin (bR) molecules at the free interface of the crystalline phase that occurs naturally in purple membrane.Our results reveal temporal fluctuations at the crystal edges arising from the association and dissociation of bR molecules, most predominantly pre-formed trimers. Analysis of the dissociation kinetics yields an estimate of the inter-trimer single-bond energy of -0.9 kcal/mol. Rotational motion of individual bound trimers indicates that the inter-trimer bond involves W10-W12 tryptophan residues.

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Section: Quantitative Analysis Of Intertrimer Interaction Energycontrasting

confidence: 99%

Dynamics of bacteriorhodopsin 2D crystal observed by high-speed atomic force microscopy

Yamashita

Voïtchovsky

Uchihashi

et al. 2009

Journal of Structural Biology

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“…In the first (17), the mobilities of MscL [R ϭ 25 Å (18)] and LacS [R ϭ 32 Å (19)] differ by a factor of 1.3 corresponding to the ratio of their radii. In the second (14), a 1͞R law fits correctly the data obtained by FCS and freeze-fracture electron microscopy on photo-activated, oligomerized BR.…”

Section: Resultssupporting

confidence: 65%

Lateral mobility of proteins in liquid membranes revisited

Gambin

López-Esparza

Reffay

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

352

377

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The biological function of transmembrane proteins is closely related to their insertion, which has most often been studied through their lateral mobility. For >30 years, it has been thought that hardly any information on the size of the diffusing object can be extracted from such experiments. Indeed, the hydrodynamic model developed by Saffman and Delbrü ck predicts a weak, logarithmic dependence of the diffusion coefficient D with the radius R of the protein. Despite widespread use, its validity has never been thoroughly investigated. To check this model, we measured the diffusion coefficients of various peptides and transmembrane proteins, incorporated into giant unilamellar vesicles of 1-stearoyl-2-oleoylsn-glycero-3-phosphocholine (SOPC) or in model bilayers of tunable thickness. We show in this work that, for several integral proteins spanning a large range of sizes, the diffusion coefficient is strongly linked to the protein dimensions. A heuristic model results in a Stokes-like expression for D, (D ؔ 1͞R), which fits literature data as well as ours. Diffusion measurement is then a fast and fruitful method; it allows determining the oligomerization degree of proteins or studying lipid-protein and protein-protein interactions within bilayers.bilayers ͉ transmembrane proteins ͉ diffusion ͉ peptides ͉ sponge phase I n the hydrodynamic model of Saffman and Delbrück (1), transmembrane peptides and proteins are described as diffusing in a perfectly continuous medium, ignoring the finite size of the lipids. This model predicts that the diffusion coefficient D of a simple cylinder embedded in a thin sheet of fluid matching its height ( Fig. 1) is given byIn this expression, the adjustable parameters are by order of importance: the thickness h and viscosity m of the liquid membrane, the radius R of the diffusing cylinder, and the viscosity of the surrounding aqueous phase w . This result follows from solving the flow field in the membrane and in the surrounding fluid, assuming no-slip boundary conditions at the surface of the cylinder, which is considered as large compared with the bilayer components (i.e., R Ͼ h). Numerous biological studies, both in model systems (2-4) and living cells (5, 6), refer to this continuum approach (7). Because D depends only weakly on R, the characterization of protein or rafts radii is delicate (8); for example, increasing the radius from 10 to 100 Å changes the mobility by a mere 30% [for h ϭ 30 Å and m ϭ 10 poise (P; 1 P ϭ 0.1 Pa⅐s)].To check the applicability of the Saffman-Delbrück formula (Eq. 1), we have used fringe pattern photobleaching under the microscope (9) to measure precisely the self-diffusion of transmembrane peptides and proteins of well characterized dimensions. Results and DiscussionThe weight of the bilayer thickness, h, has never been investigated. Rather than using lipids of various lengths, we opted for a unique system where the bilayer thickness can be continuously tuned, leaving the bilayer viscosity constant.We use a phase of model bilayers made of nonionic ...

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“…In the Gibbs formulation some of the physical consequences of the force-dipole model become clearer than in the semi-microscopic formulation. One of these consequences is an influence of the activity on the tension of the membrane, which is discussed in section V. Another consequence of the force-dipole model, discussed in section VI, is a hydrodynamic interaction force between the membrane proteins induced by the activity, offering a possible explanation of two experiments reported in [10] on the clustering and diffusion of active bacteriorhodopsin molecules. A conclusion is given in section VII, and finally an appendix is added where the bulk hydrodynamics is solved directly for the semi-microscopic formulation in the case of a nearly planar membrane.…”

Section: Introductionmentioning

confidence: 94%

Mechanics of nonplanar membranes with force-dipole activity

Lomholt

2006

Phys. Rev. E

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A study is made of how active membrane proteins can modify the long wavelength mechanics of fluid membranes. The activity of the proteins is modelled as disturbing the protein surroundings through non-local force distributions of which a force-dipole distribution is the simplest example. An analytic expression describing how the activity modifies the force-balance equation for the membrane surface is obtained in the form of a moment expansion of the force distribution. This expression allows for further studies of the consequences of the activity for non-planar membranes. In particular the active contributions to mechanical properties such as tension and bending moments become apparent. It is also explained how the activity can induce a hydrodynamic attraction between the active proteins in the membrane.

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Spatial Organization of Bacteriorhodopsin in Model Membranes

Cited by 53 publications

References 46 publications

Dynamics of bacteriorhodopsin 2D crystal observed by high-speed atomic force microscopy

Dynamics of bacteriorhodopsin 2D crystal observed by high-speed atomic force microscopy

Lateral mobility of proteins in liquid membranes revisited

Mechanics of nonplanar membranes with force-dipole activity

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