title: Identification of a lumenal sequence specifying the assembly of Emp24p into p24 complexes in the yeast secretory pathway.
abstract: The p24 proteins are transmembrane proteins of the endomembrane system that play a poorly defined role in vesicle traffic between the endoplasmic reticulum and the Golgi apparatus. Various lines of evidence indicate that p24 proteins fall into four subfamilies (alpha, beta, gamma, and delta) and that tetramers are assembled containing one representative from each subfamily; however, the nature of the protein-protein interactions within these hetero-oligomers is unknown. We have identified a lumenal segment of yeast p24beta (Emp24p) that is necessary for its assembly into p24 complexes. Replacement of 52 C-terminal residues of Emp24p with the corresponding sequence from Erv25p (p24delta) generates a chimeric protein able to replace Emp24p in p24 complexes that retain partial function in vivo, ruling out a role for the transmembrane and cytosolic domains in specifying p24 interactions. Substitution of a further 50 residues, encompassing a heptad repeat region, abolishes the ability of the chimera to replace Emp24p but instead creates a protein that resembles its Erv25p parent in its requirement for stabilization by Emp24p. These data point to a role for coiled-coil interactions in directing subfamily-specific assembly of p24 oligomers that project into the lumen of transport vesicles, where they may act to exclude secretory cargo from coat protein complex type I-coated retrograde transport vesicles.
authors.affiliation: Department of Biomedical Sciences, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh EH8 9XD, United Kingdom.
authors.forename: L F
authors.initials: LF
authors.lastname: Ciufo
authors.forename: A
authors.initials: A
authors.lastname: Boyd
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D016764:Cell Polarity; D017124:Conserved Sequence; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D033921:Vesicular Transport Proteins; D015003:Yeasts / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; C093262:EMP24 protein, S cerevisiae; C102179:ERV25 protein, S cerevisiae; D005656:Fungal Proteins; D008565:Membrane Proteins; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins