On the role of external force of actin filaments in the formation of tubular protrusions of closed membrane shapes with anisotropic membrane components

Abstract

Biological membranes are composed of different components and there is no a priori reason to assume that all components are isotropic. It was previously shown that the anisotropic properties of membrane components may explain the stability of membrane tubular protrusions even without the application of external force. Our theoretical study focuses on the role of anisotropic membrane components in the stability of membrane tubular structures generated or stabilized by actin filaments. We show that the growth of the actin cytoskeleton inside the vesicle can induce the partial lateral segregation of different membrane components. The entropy of mixing of membrane components hinders the total lateral segregation of the anisotropic and isotropic membrane components. Self-assembled aggregates formed by anisotropic membrane components facilitate the growth of long membrane tubular protrusions. Protrusive force generated by actin filaments favors strong segregation of membrane components by diminishing the opposing effect of mixing entropy.

Curving Cells Inside and Out: Roles of BAR Domain Proteins in Membrane Shaping and Its Cellular Implications

“…Interestingly, epsin, which interacts with membrane only through its AH, is a curvature sensor both on tubes (Capraro et al 2010) and spherical vesicles (Madsen et al 2010).There is, in fact, a structural difference at the molecular level in the way BAR proteins interact with spherical as opposed to tubular membranes. On tubes, proteins are able to collectively tilt their long axis to match their curvature to that of the tube(Mesarec et al 2017) thereby maintaining close contact; thus, the backbone and amphipathic helices contribute to curvature sensing, but the helices are not indispensable. In contrast, on spheres such tilting is not possible (without deforming the membrane), the backbone is not in contact, and as a result only the helices participate in curvature sensing.…”

Assembling of Topological Defects at Neck‐Shaped Membrane Parts

“…One “natural” parameter that can robustly trigger neck formation is the reduced volume v = V / V 0 . Here, V stands for the volume of the shape, and V 0 = 4 πR 3 /3 is the volume of a spherical surface of the same surface area A and radius . All lengths in our model are scaled with respect to R , which represents a typical linear dimension of the shape.…”

Modeling membrane nanotube morphology: the role of heterogeneity in composition and material properties

“…Therefore we ignore the influence of anisotropic membrane inclusions such as BIN-Amphiphysin-Rvs (BAR) domain proteins [41,40,66]. -We do not consider the role of forces applied by actin-mediated nanotube formation [40], so that we can focus only on membrane nanotube deformation due to membrane-protein interactions [67][68][69]. -For simplicity in the numerical simulations, we assume that the membrane in the region of interest is rotationally symmetric and long enough so that boundary effects are ignored ( Fig.…”

“…Recently, a series of elegant modeling studies have proposed the idea that curved proteins and cytoskeletal proteins can induce protrusions along the membrane [39][40][41][42][43]. Separately, experiments are beginning to demonstrate that (a) the composition of a membrane nanotube is not homogeneous [44]; (b) tension due to adhesion of rolling neutrophils can lead to tether formation [44]; and (c) spontaneous curvature along a nanotube can lead to the formation of bead like structures [44-47, 17, 20].…”