Abstact

Adaptor proteins load transmembrane protein cargo into transport vesicles and serve as nexuses for the formation of large multiprotein complexes on the nascent vesicles. The gamma-adaptin ear (GAE) domains of the AP-1 adaptor protein complex and the GGA adaptor proteins recruit accessory proteins to these multiprotein complexes by binding to a hydrophobic motif. We determined the structure of the GAE domain of human GGA3 in complex with a peptide based on the DFGPLV sequence of the accessory protein Rabaptin-5 and refined it at a resolution of 2.2 A. The leucine and valine residues of the peptide are partly buried in two contiguous shallow, hydrophobic depressions. The anchoring phenylalanine is buried in a deep pocket formed by the aliphatic portions of two conserved arginine residues, along with an alanine and a proline, illustrating the unusual function of a cluster of basic residues in binding a hydrophobic motif.