title: Suppression of coatomer mutants by a new protein family with COPI and COPII binding motifs in Saccharomyces cerevisiae.
abstract: Protein trafficking is achieved by a bidirectional vesicle flow between the various compartments of the eukaryotic cell. COPII coated vesicles mediate anterograde protein transport from the endoplasmic reticulum to the Golgi apparatus, whereas retrograde Golgi-to-endoplasmic reticulum vesicles use the COPI coat. Inactivation of COPI vesicle formation in conditional sec21 (gamma-COP) mutants rapidly blocks transport of certain proteins along the early secretory pathway. We have identified the integral membrane protein Mst27p as a strong suppressor of sec21-3 and ret1-1 mutants. A C-terminal KKXX motif of Mst27p that allows direct binding to the COPI complex is crucial for its suppression ability. Mst27p and its homolog Yar033w (Mst28p) are part of the same complex. Both proteins contain cytoplasmic exposed C termini that have the ability to interact directly with COPI and COPII coat complexes. Site-specific mutations of the COPI binding domain abolished suppression of the sec21 mutants. Our results indicate that overexpression of MST27 provides an increased number of coat binding sites on membranes of the early secretory pathway and thereby promotes vesicle formation. As a consequence, the amount of cargo that can bind COPI might be important for the regulation of the vesicle flow in the early secretory pathway.
authors.affiliation: Friedrich Miescher Laboratorium der Max Planck Gesellschaft, D-72076 Tübingen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Sandmann
authors.forename: Johannes M
authors.initials: JM
authors.lastname: Herrmann
authors.forename: Jörn
authors.initials: J
authors.lastname: Dengjel
authors.forename: Heinz
authors.initials: H
authors.lastname: Schwarz
authors.forename: Anne
authors.initials: A
authors.lastname: Spang
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D022181:COP-Coated Vesicles / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D003001:Cloning, Molecular; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D005838:Genotype; D006056:Golgi Apparatus / Q000235:genetics / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D011485:Protein Binding; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000648:ultrastructure; D014617:Vacuoles / Q000502:physiology / Q000648:ultrastructure
chemical_list: D008565:Membrane Proteins