Toward Structural Characterization of the Dsl1/α-COP Interaction

Abstract

Intracellular vesicular transport is an essential process by which proteins and lipids are trafficked throughout the cell. The general mechanism of transport involves four highly regulated steps: (1) vesicle budding from the donor membrane, (2) movement along the cytoskeleton toward the acceptor membrane, (3) tethering and docking at the acceptor membrane, and (4) membrane fusion. Tethering factors are a class of proteins that are reported to tether vesicle coats, uncoat vesicles, and facilitate SNARE complex assembly. Here, we investigate the interaction between Dsl1, the simplest (architecturally) tethering factor, and the COPI coat. The Dsl1 complex comprises three subunits: Dsl1, Sec39, and Tip20. The complex has a tower-like structure in which Sec39 and Tip20 form the base of the complex. Dsl1, at the apex of the tower, bridges Sec39 and Tip20. Within the Dsl1 subunit is an unstructured region, known as the lasso, to which interactions with the COPI coat have been mapped. The lasso mediates interactions with coatomer subunits α- COP and δ-COP via a tryptophan motif. In order to better understand how Dsl1 interacts with the COPI coat, we used gel filtration to validate interactions between Dsl1 and α- COP. We substituted tryptophan residue(s) within the lasso and used these mutant lasso proteins in binding experiments. We demonstrate that W425 has a critical role in the Dsl1/α-COP interaction. Here, we describe our efforts to determine the structure of Dsl1 bound to α-COP. Preliminary crystals have been obtained.