Structural basis for Rab6 activation by the Ric1-Rgp1 complex

• Published in: Nature communications 2024-12, Vol.15 (1), p.10561-13, Article 10561
• Main Authors: Feathers, J. Ryan, Vignogna, Ryan C., Fromme, J. Christopher
• Format: Article
• Language: English
• Subjects: 101/28; 14; 14/19; 631/535/1258/1259; 631/80/313/1525; 631/80/313/2011; 82/83; 96; Arrestin; Binding; Cell activation; Cryoelectron Microscopy; Electron microscopy; Eukaryotes; Golgi Apparatus - metabolism; Golgi cells; Guanine Nucleotide Exchange Factors - chemistry; Guanine Nucleotide Exchange Factors - genetics; Guanine Nucleotide Exchange Factors - metabolism; Homeostasis; Humanities and Social Sciences; Humans; Localization; Membrane trafficking; Models, Molecular; Molecular biology; Molecular machines; multidisciplinary; Nucleotides; Protein Binding; Protein Domains; Proteins; rab GTP-Binding Proteins - chemistry; rab GTP-Binding Proteins - genetics; rab GTP-Binding Proteins - metabolism; Saccharomyces cerevisiae Proteins - chemistry; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Science; Science (multidisciplinary); Structure-function relationships; Yeast
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-54869-9

Rab GTPases act as molecular switches to regulate organelle homeostasis and membrane trafficking. Rab6 plays a central role in regulating cargo flux through the Golgi and is activated via nucleotide exchange by the Ric1-Rgp1 protein complex. Ric1-Rgp1 is conserved throughout eukaryotes but the structural and mechanistic basis for its function has not been established. Here we report the cryoEM structure of a Ric1-Rgp1‐Rab6 complex representing a key intermediate of the nucleotide exchange reaction. Ric1-Rgp1 interacts with the nucleotide-binding domain of Rab6 using an uncharacterized helical domain, which we establish as a RabGEF domain by identifying residues required for Rab6 activation. Unexpectedly, the complex uses an arrestin fold to interact with the Rab6 hypervariable domain, indicating that interactions with the unstructured C-terminal regions of Rab GTPases may be a common binding mechanism used by their activators. Collectively, our findings provide a detailed mechanistic understanding of regulated Rab6 activation at the Golgi. Rab6 is a key regulator of the Golgi apparatus, the central sorting organelle of eukaryotic cells. Here the authors use cryo-electron microscopy and functional experiments to reveal how Rab6 is activated by the Ric1-Rgp1 complex.