PknG Protein of Mycobacterium tuberculosis Targets RGDI-1 to Regulate Rab7l1 GTPase Activity

The protein kinase G (PknG) protein of Mycobacterium tuberculosis is known to disrupt phagosome-lysosome (P-L) fusion, enabling the bacteria to persist within the host. In our previous study, we demonstrated that PknG inhibits GTPase activity of Rab7l1 by interacting with its inactive form (Rab7l1-GDP) to block the Rab7l1-GDP/GTP transition. As a result, the active Rab7l1 protein fails to localize onto the phagosome, which prevents recruitment of downstream P-L fusion markers like Rab7l1, EEA1, LAMP1, and LAMP2 to the phagosome, leading to inhibition of P-L fusion. In this study, we show that Rho GDP dissociation inhibitor-1 (RGDI-1) is a GDP dissociation inhibitor (GDI) for Rab7l1. RGDI-1 associates with Rab7l1 and forms a stable complex in the presence of PknG. Rab7l1 serves as a scaffold that brings together both PknG and RGDI-1, allowing PknG to interact and phosphorylate RGDI-1. Kinasing of RGDI-1 prevents its dissociation from Rab7l1, resulting in decreased activity of Rab7l1 GTPase in PMA-induced THP-1 cells. Thus, PknG prevents release of RGDI-1 from Rab7l1, leading to reduced Rab7l1 GTPase activity. When RGDI-1 is absent, PknG fails to inhibit P-L fusion, resulting in decreased mycobacterial survival inside the PMA-induced THP-1 cells. Our data suggest that PknG targets RGDI-1 to inhibit Rab7l1-mediated P-L fusion and thereby promotes mycobacterial survival inside the PMA-induced THP-1 cells.