The phagosome proteome: Insight into phagosome functions

Phagosomes are key organelles for the innate ability of macrophages to part icipate in tissue remodeling, clear apoptotic cells, and restrict the sprea d of intracellular pathogens. To understand the functions of phagosomes, we initiated the systematic identification of their proteins. Using a proteom ic approach, we identified > 140 proteins associated with latex bead-contai ning phagosomes. Among these were hydrolases, proton pump ATPase subunits, and proteins of the fusion machinery, validating our approach. A series of un expected proteins not previously described along the endocytic/phagocyti c pathways were also identified, including the apoptotic proteins galectin3 , Alix, and TRAIL, the anti-apoptotic protein 14-3-3, the lipid raft-enrich ed flotillin-1, the anti-microbial molecule lactadherin, and the small GTPa se rab14. In addition, 24spots from which the peptide masses could not be m atched to entries in any database potentially represent new phagosomal prot eins. The elaboration of a two-dimensional gel database of > 160 identified spots allowed us to analyze how phagosome composition is modulated during phagolysosome biogenesis. Remarkably, during this process, hydrolases are n ot delivered in bulk to phagosomes, but are instead acquired sequentially. The systematic characterization of phagosome proteins provided new insights into phagosome functions and the protein or groups of proteins involved in and regulating these functions.