Electrostatics of Lipid Bilayer Bending

TL;DR

This paper calculates the electrostatic contribution to membrane curvature using Poisson-Boltzmann theory, showing how surface charges and screening layers influence vesicle bending and potential tubule formation.

Contribution

It introduces a detailed electrostatic model for membrane bending, including effects of asymmetric charges and charge conservation, expanding understanding of membrane mechanics.

Findings

Electrostatic effects can induce membrane bending with radii of 50-100nm.

Asymmetric surface charges produce opposite curvature signs.

Electrostatic contribution to bending modulus is generally small.

Abstract

The electrostatic contribution to spontaneous membrane curvature is calculated within Poisson-Boltzmann theory under a variety of assumptions and emphasizing parameters in the physiological range. Asymmetric surface charges, either fixed with respect to bilayer midplane area, or with respect to the lipid-water area both induce curvature but of opposite sign. Unequal screening layers on the two sides of a vesicle ({\it e.g.} multivalent cationic proteins on one side and monovalent salt on the other) also induces bending. For reasonable parameters, tubules formed by electrostatically induced bending can have radii in the 50-100nm range, often seen in many intracellular organelles. Thus membrane associated proteins may induce curvature and subsequent budding, without themselves being intrinsically curved. Furthermore, we derive the previously unexplored effects of respecting the strict conservation of charge within the interior of a vesicle. The electrostatic component to the bending modulus is small under most of our conditions, and is left as an experimental parameter. The large parameter space of conditions is surveyed in an array of graphs.