Jan 16, 2020

Structure and activation mechanism of the BBSome membrane protein trafficking complex

ELife
Sandeep K SinghAlan Brown

Abstract

Bardet-Biedl syndrome (BBS) is a currently incurable ciliopathy caused by the failure to correctly establish or maintain cilia-dependent signaling pathways. Eight proteins associated with BBS assemble into the BBSome, a key regulator of the ciliary membrane proteome. We report the electron cryomicroscopy (cryo-EM) structures of the native bovine BBSome in inactive and active states at 3.1 -and 3.5 Å resolution, respectively. In the active state, the BBSome is bound to an Arf-family GTPase (ARL6/BBS3) that recruits the BBSome to ciliary membranes. ARL6 recognizes a composite binding site formed by BBS1 and BBS7 that is occluded in the inactive state. Activation requires an unexpected swiveling of the b-propeller domain of BBS1, the subunit most frequently implicated in substrate recognition, which widens a central cavity of the BBSome. Structural mapping of disease-causing mutations suggests that pathogenesis results from folding defects and the disruption of autoinhibition and activation.

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References

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Citations

Mentioned in this Paper

ARL6 gene
Arl3 protein, Drosophila
ARL6 protein, human
Bregma
Signal Pathways
Electron Microscopy
Bardet-Biedl Syndrome
Cryoelectron Microscopy
BBS1
Protein Domain

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