Two intramolecular interfaces control the WDR44 conformational switch that regulates Rab11 binding

The Rab11 protein is crucial for two distinct membrane trafficking pathways, namely endocytic recycling and preciliary trafficking to the centriole. The Rab11 effector WDR44 plays a key role in promoting the former pathway, yet suppresses ciliogenesis in serum-grown cells. WDR44 interacts with Rab11 through a N-terminal domain that is autoinhibited by an intramolecular interaction with the C-terminal WD40 domain. However, the exact mechanism by which this closed conformation is maintained remained unclear.

To elucidate this process, the researchers employed structural modeling, mutational analysis, and a bystander BRET assay designed to monitor WDR44 recruitment to Rab11 compartments in live cells. The investigation identified two N-terminal segments that engage with distinct surfaces of the WD40 domain. The larger segment extends along the top face of the domain, a region where pathogenic variants associated with ciliopathies are frequently found. In contrast, a second segment interacts with the side of the WD40 domain.

Disrupting either of these N-terminal segments weakens the intramolecular interaction, thereby facilitating WDR44 recruitment to Rab11 compartments. By defining the contacts that sustain WDR44 in its closed conformation, this study sheds light on the mechanism through which pathogenic mutations could potentially alter WDR44 function, thus providing new insights into the regulation of Rab11 and its downstream effects on membrane trafficking pathways.