Abstract
The Rab GTPase family is a major regulator of membrane traffic in eukaryotic cells. The Rab11 subfamily plays important roles in specific trafficking events such as exocytosis, endosomal recycling, and cytokinesis. SH3BP5 and SH3BP5-like (SH3BP5L) proteins have recently been found to serve as guanine nucleotide exchange factors (GEF) for Rab11. Here, we report the crystal structures of the SH3BP5 GEF domain alone and its complex with Rab11a. SH3BP5 exhibits a V-shaped structure comprising two coiled coils. The coiled coil composed of α1, and α4 is solely responsible for the Rab11a binding and GEF activity. SH3BP5 pulls out and deforms switch I of Rab11a so as to facilitate the GDP release from Rab11a. SH3BP5 interacts with the N-terminal region, switch I, interswitch, and switch II of Rab11a. SH3BP5 and SH3BP5L localize to Rab11-positive recycling endosomes and show GEF activity for all of the Rab11 family but not for Rab14. Fluorescence-based GEF assays combined with site-directed mutagenesis reveal the essential interactions between SH3BP5 and Rab11 family proteins for the GEF reaction on recycling endosomes.
Highlights
The Rab family is the largest small GTPase family of the Ras superfamily
We revealed that the V-shaped SH3-binding protein 5 (SH3BP5) promotes the nucleotide release from Rab11a by inducing a drastic conformational change of the nucleotide-binding pocket of Rab11a
We further identified key residues of human SH3BP5 and Rab11a for the nucleotide exchange reaction
Summary
The Rab family is the largest small GTPase family of the Ras superfamily. More than 60 Rab proteins have been identified in human. They are major regulators of membrane traffic [1]. Each Rab protein shows distinctive localizations in plasma membrane and/or organelles such as endosomes, Golgi, and lysosome. Rab is reversibly anchored to membranes by the posttranslational geranylgeranylation of the C-terminal cysteine residues. The membrane-anchored Rab proteins serve as identity markers for membrane compartments and control the downstream events in membrane traffic
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