Fromme Lab

Happy Halloween! #GhostlyGolgi

Taken together, our findings allow us to model the orientation of Ric1-Rgp1 on the Golgi membrane and understand how it activates Rab6. (8/9)

Ryan also identified a conserved amphipathic alpha-helix within Rgp1 that is flexibly linked to the bulk of the complex and likely plays a role in membrane binding. Removal of this helix significantly reduces the Golgi localization of the complex in cells. (7/9)

Our lab previously determined that two other RabGEF complexes, TRAPPII and TRAPPIII, also use the HVDs of their substrates as specificity determinants, suggesting that HVD binding may be common among GEFs. (6/9)

Surprisingly, the unstructured C-terminal HVD of Rab6 binds to a conserved surface of the Rgp1 arrestin fold. Ryan found the Rab6 HVD sequence is important for activation in cells, indicating that the HVD is a specificity determinant used by Ric1-Rgp1 to identify Rab6. (5/9)

Ryan identified key residues in the GEF domain and found they are essential for GEF activity in an in vitro reconstitution system utilizing purified proteins, prenylated Rab6-GDI substrate, and synthetic liposome membranes. (4/9)

The Ric1 subunit possesses a novel GEF domain that dramatically remodels the Rab6 nucleotide binding site to release GDP. (3/9)

Rab6 is activated by its GEF, the Ric1-Rgp1 complex, but it is unknown how this complex performs nucleotide exchange to activate Rab6. Ryan’s structure reveals the architecture of the complex and provides a mechanistic explanation for Ric1-Rgp1 function. (2/9)

We are excited to share a new preprint from the lab! Rab6 is a central regulator of the Golgi, important for trafficking and autophagy. @FeathersRyan used #cryoEM to determine the structural basis of the Rab6 activation process. (1/9)

@BrownfieldBryce performed extensive functional experiments guided by both the experimental and #AlphaFold predicted conformations. Taken together, the structural and functional results lead us to model explaining how Sec7 transitions from the autoinhibited to active states.

The structure reveals the organization of the regulatory domains. Despite many similarities in primary sequence, the structure of the Sec7 homodimer is strikingly different from that of the GBF1-family member Gea2, determined previously in our lab by @ArnoldMuccini.