Cells use a process called phagocytosis to capture and degrade large particles, such as microorganisms, inside special packages. These special packages, called phagosomes, pinch off the cellular plasma membrane and are dynamic entities that mature inside cells as they break down their contents. But how do the membranes of phagosomes arrange themselves during the process? Some studies have hinted that phagosomes’ membranes may contain lipid rafts, which are microdomains initially thought to be unique to the plasma membrane. In a recent Molecular & Cellular Proteomics paper, Michel Desjardins at the University of Montreal in Canada and colleagues used both proteomics and bioinformatics to carry out a large-scale characterization of the spatiotemporal changes that occurred during three stages of the phagosomal maturation process, focusing on the proteins associated with lipid rafts (1). They saw that the membrane microdomains in phagosomes assembled late in the maturation process. The finding was surprising to the investigators, as they expected the microdomains to be acquired early from the plasma membrane, where these structures are enriched and well organized, explains Desjardins. The investigators went on to find that many of the proteins within microdomains at later stages were indeed present in less mature phagosomes but were found in other parts of the membrane. Desjardins explains that the data indicate the membrane is actively reorganized to assemble the lipid rafts during phagosome maturation. He adds that one future direction of the study will be to investigate how pathogens like Leishmania, Brucella and Mycobacterium can disrupt the formation of lipid rafts to inhibit the phagocytotic process.
- 1) Guillaume Goyette, et al. Mol. Cell. Proteomics. doi: 10.1074/mcp.M112.021048 (2012)
Rajendrani Mukhopadhyay (firstname.lastname@example.org) is the senior science writer for ASBMB Today and the technical editor for The Journal of Biological Chemistry. Follow her on Twitter (www.twitter.com/rajmukhop).