Biochemical and structural insights into Rab12 interactions with RILP and its family members

Abstract

Alongside its biosynthetic functions, the small GTPase Rab12 negatively regulates mast cell (MC) exocytosis by its interaction with RILP to promote retrograde transport of the MC secretory granules. Given the role of Rab effectors in mediating Rab functions, in this study we used biochemical and in silico tools to decipher Rab12 interactions with its RILP family effectors. We show that Rab12 interacts with RILP, RILP-L1 and RILP-L2 independently of each other, whereby lysine-71, in mouse Rab12, is critical for Rab12 interactions with RILP-L1 or RILP-L2, but is dispensable for the binding of RILP. Focusing on RILP, and relying on molecular dynamics simulations, functional mutational analyses and peptide inhibition assays, we propose a model for the Rab12-RILP complex, consisting of a RILP homodimer and a single molecule of active Rab12, that interacts with the RILP homology domain (RHD) of one RILP monomer and a C-terminal threonine in the other monomer via its switch I and switch II regions. Mutational analyses of RILP RHD also demonstrate its involvement in the regulation of MC secretory granule transport. Jointly, our results provide structural and functional insights into the Rab12-RILP complex on the basis of which new tools could be generated for decoding Rab12 functions.

Host Cell Signatures of the Envelopment Site within Beta-Herpes Virions

“…Rab12 localizes to the EEs and ERC and controls the transport of specific cargo, such as TfR, from the ERC to lysosomes [ 125 ] and stimulates autophagy [ 131 ], autophagosome trafficking [ 132 ], and retrograde transport from the ERC to TGN [ 133 ]. It has been suggested that Rab12 facilitates the direct or indirect fusion of RE/ERC-derived compartments with lysosomes [ 125 ] and links autophagosomes to motor proteins to facilitate autophagosome trafficking [ 132 ].…”