title: Localization and recycling of gp27 (hp24gamma3): complex formation with other p24 family members.
abstract: We report here the characterization of gp27 (hp24gamma3), a glycoprotein of the p24 family of small and abundant transmembrane proteins of the secretory pathway. Immunoelectron and confocal scanning microscopy show that at steady state, gp27 localizes to the cis side of the Golgi apparatus. In addition, some gp27 was detected in COPI- and COPII-coated structures throughout the cytoplasm. This indicated cycling that was confirmed in three ways. First, 15 degrees C temperature treatment resulted in accumulation of gp27 in pre-Golgi structures colocalizing with anterograde cargo. Second, treatment with brefeldin A caused gp27 to relocate into peripheral structures positive for both KDEL receptor and COPII. Third, microinjection of a dominant negative mutant of Sar1p trapped gp27 in the endoplasmic reticulum (ER) by blocking ER export. Together, this shows that gp27 cycles extensively in the early secretory pathway. Immunoprecipitation and coexpression studies further revealed that a significant fraction of gp27 existed in a hetero-oligomeric complex. Three members of the p24 family, GMP25 (hp24alpha2), p24 (hp24beta1), and p23 (hp24delta1), coprecipitated in what appeared to be stochiometric amounts. This heterocomplex was specific. Immunoprecipitation of p26 (hp24gamma4) failed to coprecipitate GMP25, p24, or p23. Also, very little p26 was found coprecipitating with gp27. A functional requirement for complex formation was suggested at the level of ER export. Transiently expressed gp27 failed to leave the ER unless other p24 family proteins were coexpressed. Comparison of attached oligosaccharides showed that gp27 and GMP25 recycled differentially. Only a very minor portion of GMP25 displayed complex oligosaccharides. In contrast, all of gp27 showed modifications by medial and trans enzymes at steady state. We conclude from these data that a portion of gp27 exists as hetero-oligomeric complexes with GMP25, p24, and p23 and that these complexes are in dynamic equilibrium with individual p24 proteins to allow for differential recycling and distributions.
authors.affiliation: Cell Biology and Cell Biophysics Program, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Füllekrug
authors.forename: T
authors.initials: T
authors.lastname: Suganuma
authors.forename: B L
authors.initials: BL
authors.lastname: Tang
authors.forename: W
authors.initials: W
authors.lastname: Hong
authors.forename: B
authors.initials: B
authors.lastname: Storrie
authors.forename: T
authors.initials: T
authors.lastname: Nilsson
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D020126:Brefeldin A / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D037241:Mannose-Binding Lectins; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins; D028861:Nuclear Pore Complex Proteins; D009844:Oligosaccharides / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D018000:Receptors, Peptide / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D014759:Viral Envelope Proteins / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D005656:Fungal Proteins; C028391:G protein, vesicular stomatitis virus; D006023:Glycoproteins; C064459:KDEL receptor; C084004:LMAN1 protein, human; D037241:Mannose-Binding Lectins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D028861:Nuclear Pore Complex Proteins; D009844:Oligosaccharides; D010750:Phosphoproteins; D018000:Receptors, Peptide; D011994:Recombinant Proteins; C079620:SEC13 protein, S cerevisiae; C106113:SEC31 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D014759:Viral Envelope Proteins; D020126:Brefeldin A; D019204:GTP-Binding Proteins; D020559:Monomeric GTP-Binding Proteins; C077395:SAR1 protein, S cerevisiae