Rab11FIP proteins link endocytic recycling vesicles for cytoskeletal transport and tethering.

Regulated trafficking of internalised integrins and growth factor receptors enables polarisation of morphology and motility and enables lumen formation in multicellular structures. Recycling vesicles marked with Rab11 direct internalised cargo back to the plasma membrane to affect biological processes such as polarised trafficking and cancer cell invasion. A recent study by Ji and colleagues, provides insight into how the trafficking protein Rab11FIP2 links with the actin-based motor myo5b and the small GTPase Rab11 to regulate vesicle tethering and transport along actin filaments [1]. The authors used biochemical methods to demonstrate that Rab11a binds directly to the tail of myo5b and that Rab11FIP2 also forms direct interactions with both Rab11a and myo5b tails. These proteins essentially compete for binding to similar regions and thus can regulate the association and activity of each other. Ji and colleagues further demonstrate that Rab11a activates myo5b by binding to its globular tail and relieving a head-tail autoinhibition. Due to differing affinities between Rab11 and myo5b or Rab11FIP2, they propose that Rab11FIP2 mediates the association of myo5b with cargo vesicles, while Rab11a regulates the motor activity of myo5b. The present study thus elucidates how myo5b is regulated by its interactions with Rab11a and Rab11FIP2 and proposes a model for coordination of recycling vesicle tethering and motor activity. The present study has implications for how cells control polarity and motility in health and disease and suggests how Rab11FIP proteins might control motor protein activity and engagement for transport.