The pentameric WASH complex facilitates endosomal protein sorting by activating Arp2/3, which in turn leads to the formation of F‐actin patches specifically on the endosomal surface. It is generally accepted that WASH complex attaches to the endosomal membrane via the interaction of its subunit FAM21 with the retromer subunit VPS35. However, we observe the WASH complex and F‐actin present on endosomes even in the absence of VPS35. We show that the WASH complex binds to the endosomal surface in both a retromer‐dependent and a retromer‐independent manner. The retromer‐independent membrane anchor is directly mediated by the subunit SWIP. Furthermore, SWIP can interact with a number of phosphoinositide species. Of those, our data suggest that the interaction with phosphatidylinositol‐3,5‐bisphosphate (PI(3,5)P2) is crucial to the endosomal binding of SWIP. Overall, this study reveals a new role of the WASH complex subunit SWIP and highlights the WASH complex as an independent, self‐sufficient trafficking regulator.

The pentameric WASH complex facilitates endosomal protein sorting by activating Arp2/3, which in turn leads to the formation of F-actin patches specifically on the endosomal surface. It is generally accepted that WASH complex attaches to the endosomal membrane via the interaction of its subunit FAM21 with the retromer subunit VPS35. However, we observe the WASH complex and F-actin present on endosomes even in the absence of VPS35. We show that the WASH complex binds to the endosomal surface in both a retromer-dependent and a retromer-independent manner. The retromer-independent membrane anchor is directly mediated by the subunit SWIP. Furthermore, SWIP can interact with a number of phosphoinositide species. Of those, our data suggest that the interaction with phosphatidylinositol-3,5-bisphosphate (PI(3,5)P2) is crucial to the endosomal binding of SWIP. Overall, this study reveals a new role of the WASH complex subunit SWIP and highlights the WASH complex as an independent, self-sufficient trafficking regulator.

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