Curvature sorting of proteins on a cylindrical lipid membrane tether connected to a reservoir

Abstract

Membrane curvature of a biological cell is actively involved in various fundamental cell biological functions. It has been discovered that membrane curvature and binding of peripheral membrane proteins follow a symbiotic relationship. The exact mechanism behind this interplay of protein binding and membrane curvature has not yet been properly understood. To improve understanding of the mechanism, we study curvature sorting of proteins in a model system consisting of a tether pulled from a giant unilamellar vesicle using mechanical-thermodynamic models. The concentration of proteins bound to the membrane changes significantly due to curvature. This has also been observed in experiments by other researchers. We also find that there is a phase transition based on protein concentration and we discuss the coexistence of phases and stability of solutions. Furthermore, when sorting is favorable, the increase in protein concentration stabilizes the tether in the sense that less pulling force is required to maintain the tether. A similar mechanism may be in place, when motor proteins pull tethers from donor membranes.

Two-dimensional convex-molecule fluid model for surface adsorption of proteins: Effect of soft interaction on adsorption equilibria

“…Note also that multiple values of the packing fraction have been observed below the critical temperature, suggesting that the protein phases differ in density. Such behavior has also been observed by Singh et al [11] for sorting of proteins in a cylindrical membrane tube.…”

“…Recently, the adsorbed phase of proteins has been modeled as a two-dimensional van der Waals or Bragg-Williams gas to study the curvature sorting of proteins on a cylindrical * Corresponding author: sovandas@iitk.ac.in lipid membrane [11,12]. The hard repulsive behavior of the molecules for both these models and the other hardparticle fluid models does not capture reality well.…”

Onsager’s Variational Principle in Soft Matter: Introduction and Application to the Dynamics of Adsorption of Proteins onto Fluid Membranes

“…In the present context, it makes more sense to interpret this term as a self-interaction term of adsorbate molecules of the form −(RT /a 0 )χφ 2 plus a term proportional to φ that can be included in µ 0,a . Such a free energy has been invoked to examine equilibrium in the context of adsorption of curving proteins on lipid membranes (Sorre et al, 2012;Singh et al, 2012).…”

“…Application of a force may change the shape, inducing lipid flows that advect proteins, drive diffusion and feedback into shape. Although several models have coupled mechanical and chemical phenomena resulting from the interaction between membranes and proteins, these focus on equilibrium (Zhu et al, 2012;Singh et al, 2012;Lipowsky, 2013), on the linearized setting (Callan-Jones et al, 2016), or consider simplistic models for the mechanical relaxation dynamics (Liu et al, 2009). In this Chapter, we do not attempt to address all these requirements.…”

Bending "On the Rocks"--A Cocktail of Biophysical Modules to Build Endocytic Pathways

“…Membrane nanotubes can be pulled with controlled curvature radii, and the mechanical action of proteins on membranes can be deduced from force measurements and compared with theoretical models (Sorre et al 2012). Protein distribution can be tuned as a function of membrane curvature by continuous changing of the tube radius under concomitant observation by fluorescence microscopy (Sorre et al 2009(Sorre et al , 2012Roux et al 2010;Singh et al 2012). Membrane fission can be followed in real time and analyzed in detail Morlot et al 2012).…”