Membrane Remodeling During Viral Infection, Parasite Invasion, And Apoptosis

Child Health And Human Development

Investigators

Linked publications & trials

Abstract

This project is aimed at the understanding of the physico-chemical mechanisms of membrane remodeling during physiological and pathogenic events. There are two components: [unreadable] [unreadable] 1. Intracellular malaria parasites leave their host erythrocytes to infect neighbouring cells after each cycle of asexual replication. No method is currently available for the direct quantification of parasite release. To quantify parasite release process, human erythrocytes infected with Plasmodium falciparum were injected into sealed chambers at optimal density, where they progressed through the end of the erythrocyte cycle. Each event of parasite release inside the chamber at the site of erythrocyte rupture leaves on the chamber wall a footprint, composed of 1) separated parasites, 2) a digestive vacuole with haemozoin, and 3) fragments of the ruptured membranes. These footprints are stable for hours, allowing precise identification using differential interference contrast (DIC) microscopy. The relative rate of parasite release is defined as the percent of such footprints out of all schizonts injected and incubated into chamber at 37C for two hours. The method is highly reproducible, easy to perform, and does not require expensive equipment. Additionally, this method allows one to analyse cell and release site morphology, which adds information about the release process and the quality of the culture. The method is used here to show that swelling of schizonts caused by protein-free media inhibits parasite release.[unreadable] [unreadable] In conclusion, a novel method is described to count sites of parasite release by microscopy. Besides the direct estimation of parasite release from infected erythrocytes, this method provides a morphological evaluation of normal infected cells approaching the end of the plasmodial life cycle, or pathological forms accumulated as the result of experimental intervention in the parasite release process. One may now accurately estimate the relative parasite release rate at the time of cycle transition, without any obligatory coupling to parasite invasion.[unreadable] [unreadable] 2. The shape of enveloped viruses depends critically on an internal protein matrix, yet it remains unclear how the matrix proteins control the geometry of the envelope membrane. We found that matrix proteins, purified form Newcastle Disease Virus, adsorb on a phospholipid bilayer and condense into fluid-like domains that cause membrane deformation and budding of spherical vesicles, as seen by fluorescent and electron microscopy. Measurements of the electrical admittance of the membrane resolved the gradual growth and rapid closure of a bud, followed by its separation to form a free vesicle. The vesicle size distribution, confined by intrinsic curvature of budding domains, but broadened by their merger, matched the virus size distribution. Thus, matrix proteins implement domain-driven mechanism of budding, which suffices to control the shape of these proteolipid vesicles.