Rab coupling protein binds to phagosomes by direct interaction with Rab11.

PAVAROTTI M; LEIVA N; COLOMBO MI; DAMIANI MT

Pinamar. Buenos Aires. Argentina

Congreso; XLI Reunión Científica Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular- SAIB; 2005

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular. SAIB

Rab Coupling Protein (RCP) is a member of the newly identified class I Rab11 Family of Interacting Proteins (FIPs). RCP binds Rab11 tightly via a Rab Binding Domain located at its C-terminus. The N-end region of RCP has a C2 phospholipid-binding domain. Using confocal microscopy and biochemical assays, we have previously shown that RCP regulates phagocytosis and recycling from the phagosomal compartment in macrophages. To further characterize the binding of RCP to phagosomal membranes, we use truncated forms of this protein fused to the green fluorescent protein. The C-terminus of RCP (CT-RCP) displays a membrane-bound pattern and alters endosomal compartment. We observed CT-RCP associated as discrete patches to phagosomes. On the contrary, N-terminus of RCP (NT-RCP) has a diffuse distribution resembling a soluble protein. Neither association to early and recycling endosomes nor to early phagosomes could be observed. Stimulation of phosphatidic acid synthesis (a lipid to which RCP preferentially binds) results in the translocation of NT-RCP from the cytosol to the plasma membrane. However, we still could not observe any association of NT-RCP to early phagosomes after PMA treatment. Therefore, these results suggest that RCP is associated to phagosomes via a direct interaction with Rab11 and that the C2 domain is required to target vesicles departing from the phagosomal compartment to the plasma membrane. These events could be important for the understanding of molecular mechanisms involved in antigen presentation.