α-Hemolysin membrane pore density measured on liposomes

Abstract

Membrane pore proteins are powerful tools that allow manipulation of the inside composition of micron sized bioreactors such as artificial liposomes. While the pores self-assemble very reliably on phospholipid bilayers, the determination of the number of pores in situ for liposomes remains difficult. Here we present three independent methods to establish the number of pores on different types of liposomes: (A) the loss of refractive index due to equilibration of the inside and outside buffer conditions, and the loss of volume by (B) membrane aspiration and by (C) membrane tether pulling experiments. With these three methods we are able to determine the pore density on the membrane, and all measurements give similar values; an average pore distance is found on the order of 100 nm.