The RalB-RLIP76 Complex Reveals a Novel Mode of Ral-Effector Interaction

SummaryRLIP76 (RalBP1) is a multidomain protein that interacts with multiple small G protein families: Ral via a specific binding domain, and Rho and R-Ras via a GTPase activating domain. RLIP76 interacts with endocytosis proteins and has also been shown to behave as a membrane ATPase that transports chemotherapeutic agents from the cell. We have determined the structure of the Ral-binding domain of RLIP76 and show that it comprises a coiled-coil motif. The structure of the RLIP76-RalB complex reveals a novel mode of binding compared to the structures of RalA complexed with the exocyst components Sec5 and Exo84. RLIP76 interacts with both nucleotide-sensitive regions of RalB, and key residues in the interface have been identified using affinity measurements of RalB mutants. Sec5, Exo84, and RLIP76 bind Ral proteins competitively and with similar affinities in vitro.

Graphical AbstractFigure optionsDownload high-quality image (314 K)Download as PowerPoint slideHighlights
► The Ra1 binding coiled coil is the first structure available of RLIP/Ra1BP1
► RLIP76 interacts with the switch regions of Ra1B using a novel Ra1-binging motif
► The binding to Ra1B is different from, and competitive with, exocyst component binding
► Mutational analysis shows that RLIP76 Trp-430 is a hotspot in the interface