Neisseria gonorrhoeae porin modulates phagosome maturation

The porin (PorB) of Neisseria gonorrhoeae has been implicated in the pathogenesis of this species. Porin is believed to translocate from the bacterial outer membrane into target cell membranes affecting various cell functions. Here we investigated the effect of porin on phagosome maturation. Phagocytosis of latex beads by human macrophages was allowed in the presence or absence of purified porin. Isolation of latex bead-containing phagosomes and subsequent two-dimensional gel electrophoresis revealed substantial differences in the phagosomal protein composition. Immunoblotting detected higher amounts of annexin II and the early endocytic markers Rab5 and transferrin receptor and decreased levels of the late endocytic markers Rab7 and cathepsin D in phagosomes obtained in the presence of porin compared with those obtained in its absence. Furthermore, association of Rab4 with the latex bead-containing phagosomes was revealed by flow cytometry. The amount of this small GTPase was markedly higher in the phagosomes isolated in the presence of porin. The data thus indicate that neisserial porin is itself able to arrest phagosome maturation within macrophages.