Structural changes to host and parasite during malarial egress from the human red blood cell
Lead Research Organisation:
Birkbeck, University of London
Department Name: Biological Sciences
Abstract
Malaria impacts on the lives of about half of the world?s population and is the biggest single pathogen killer of children below the age of 5. There is no effective vaccine, and resistance to many available antimalarial drugs is spreading. There is an urgent need to find new ways of combating the disease. The malaria parasite infects and grows inside red blood cells, dividing within a membrane-bound parasitophorous vacuole. Eventually, in a rapid, highly regulated process called egress, the parasite surface is extensively modified and the vacuole and host cell membranes rupture, releasing mature forms called merozoites which immediately invade new cells. Exactly how the merozoite surface is modified to prepare it for release and invasion, and how eventual membrane rupture occurs, is unknown.
This research project has two related aims. First, we wish to understand the molecular mechanisms by which the intracellular parasite destabilises and ruptures its bounding membranes. A particular parasite enzyme called a protease is known to play a key role in this. The same protease also dramatically alters the parasite surface itself just before release, to enable it to invade new red blood cells, and so the second aim of our project is to explore the nature, importance and function of these surface protein modifications. To do this, we will apply powerful new methods for studying the three-dimensional shape and structure of isolated parasite surface molecules, and of parasite-infected cells that have been rapidly frozen to preserve them in a close to living state. By linking structural changes in molecules and membranes to functional changes, our findings will improve our understanding of these critical steps in the parasite life cycle and should shed light on new ways to fight this devastating disease.
This research project has two related aims. First, we wish to understand the molecular mechanisms by which the intracellular parasite destabilises and ruptures its bounding membranes. A particular parasite enzyme called a protease is known to play a key role in this. The same protease also dramatically alters the parasite surface itself just before release, to enable it to invade new red blood cells, and so the second aim of our project is to explore the nature, importance and function of these surface protein modifications. To do this, we will apply powerful new methods for studying the three-dimensional shape and structure of isolated parasite surface molecules, and of parasite-infected cells that have been rapidly frozen to preserve them in a close to living state. By linking structural changes in molecules and membranes to functional changes, our findings will improve our understanding of these critical steps in the parasite life cycle and should shed light on new ways to fight this devastating disease.
Technical Summary
This project has two objectives related to egress of merozoites from the Plasmodium falciparum-infected erythrocyte: (1) to determine the structural consequences and function of PfSUB1 protease-mediated proteolytic processing of the major merozoite surface protein MSP1, occurring in the early stages of egress; and (2) to define what cellular and molecular changes occur in the parasitophorous vacuole and red cell membranes leading to their rupture and merozoite release.
For objective (1) we will use single particle cryo-electron microscopy (cryo-EM) analysis and biophysical methods to establish the conformation of the merozoite surface protein MSP1 before and after proteolysis by PfSUB1. The findings will be related to merozoite infectivity.
For objective (2) we will use existing and novel pharmacological tools combined with state-of-the-art cryo-EM cellular tomography to characterize membrane changes and other structural alterations that lead to their rupture, in normal cells and under experimental conditions that stall egress at different stages.
To achieve our aims we have formed a collaborative partnership between groups with complementary strengths in malarial ultrastructure, single-molecule and cellular cryo-EM, malaria parasite biochemistry and cell biology.
For objective (1) we will use single particle cryo-electron microscopy (cryo-EM) analysis and biophysical methods to establish the conformation of the merozoite surface protein MSP1 before and after proteolysis by PfSUB1. The findings will be related to merozoite infectivity.
For objective (2) we will use existing and novel pharmacological tools combined with state-of-the-art cryo-EM cellular tomography to characterize membrane changes and other structural alterations that lead to their rupture, in normal cells and under experimental conditions that stall egress at different stages.
To achieve our aims we have formed a collaborative partnership between groups with complementary strengths in malarial ultrastructure, single-molecule and cellular cryo-EM, malaria parasite biochemistry and cell biology.