Proteins, curvature-mediated interactions

Reynwar BJ, Iliya G, Harmandaris VA, Miifler MM, Kremer K, Desemo M (2007) Aggregation and vesiculation of membrane proteins by curvature-mediated interactions. Nature 447 461 164... 

While these models have been successfully applied to curvature mediated-interactions (also in the presence of proteins or nanoparticles), thus to scales of the order of several tens (and sometimes up to hun-... 

Baumgartner and coworkers [145,146] study lipid-protein interactions in lipid bilayers. The lipids are modeled as chains of hard spheres with heads tethered to two virtual surfaces, representing the two sides of the bilayer. Within this model, Baumgartner [145] has investigated the influence of membrane curvature on the conformations of a long embedded chain (a protein ). He predicts that the protein spontaneously localizes on the inner side of the membrane, due to the larger fluctuations of lipid density there. Sintes and Baumgartner [146] have calculated the lipid-mediated interactions between cylindrical inclusions ( proteins ). Apart from the... 

These fields differ quite substantially in their theoretical description concentrations are scalar variables, orientations are vectors, and differential geometry is at heart a tensor theory but, aU of them are known to mediate interactions. For instance, the fact that proteins might prefer one lipid composition over another and thus aggregate [217-220] is central to an important mechanism attributed to lipid rafts. Tilt-mediated protein interactions have also been studied in multiple contexts [32, 33, 159, 221-223]. It is even possible to describe all these phenomena within a common language [224], using the framework of covariant surface stresses [154, 155, 157-161]. However, in the present review we will restrict the discussion to only two examples, both related to membrane elasticity in Sect. 3.1 we will discuss interactions due to hydrophobic mismatch, and in Sect. 3.2 we will look at interactions mediated by the large-scale curvature deformation of the membrane. 

When membranes fuse, the so-called stalk hypothesis suggests that the intermediate hemifusion state (Fig. 6.4c) comprises a structure in which proximal monolayers layers are connected by a bent stalk and the distal layers are pulled towards each other, thus forming a dimple (see also Fig. 6.5) The stalk model has been supported by theoretical and experimental observations. The fusion of model membranes appears to occur via the same series of fusion intermediates as those in vivo, although the approach of membranes is not Rab/SNARE mediated but is driven by reduced bilayer repulsion forces arising from hydration, electrostatic interactions, thermal fluctuations (Helfrich interaction) or osmotic stress. Membrane fusion is also promoted by defects introduced into the membrane by lateral phase separation (for example of lipid rafts, see above), high spontaneous membrane curvature, or addition of macromolecules or proteins into the membrane. 

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