Scyl1 scaffolds class II Arfs to selective subcomplexes of coatomer via the γ-COP appendage domain

Abstract

Coatomer (COPI)-coated vesicles mediate membrane trafficking in the early secretory pathway. There are at least three subclasses of COPI coats and two classes of Arf GTPases that couple COPI coat proteins to membranes. Whether mechanisms exist to link specific Arfs to selective COPI subcomplexes is unknown. We now demonstrate that Scy1-like 1 (Scyl1), a member of the Scy1-like family of catalytically inactive protein kinases oligomerizes through centrally located HEAT repeats and uses a C-terminal RKXX-COO− motif to interact directly with the appendage domain of γ2-COP. Through a distinct site, Scyl1 interacts selectively with class II Arfs, notably Arf4, thus linking class II Arfs to γ2-bearing COPI subcomplexes. Therefore, Scyl1 functions as a scaffold for key components of COPI coats and disruption of the Scyl1 scaffolding function causes tubulation of the ER/Golgi intermediate compartment and cis-Golgi, similar to that observed following loss of Arf and Arf-GEF function. Our data reveal Scyl1 as a key organizer of a selective subset of the COPI machinery.