title: COP-binding sites in p24delta2 are necessary for proper secretory cargo biosynthesis.
abstract: The p24 family is thought to be somehow involved in endoplasmic reticulum-to-Golgi protein transport, and its members are major constituents of transport vesicles and bind to the vesicle coat protein complexes COPI and COPII. A subset of the p24 proteins (p24alpha(3), -beta(1), -gamma(3) and -delta(2)) is upregulated when Xenopus laevis intermediate pituitary melanotrope cells are physiologically activated to produce vast amounts of their major secretory cargo, the prohormone proopiomelanocortin (POMC). To investigate the role of the COP-binding motifs of p24 proteins in POMC biosynthesis, we here generated and analysed Xenopus with stable, melanotrope cell-specific transgene expression of p24delta(2)-GFP mutated in its COPI- or COPII-binding motif. In contrast to what has been found previously for wild-type (wt) p24delta(2)-GFP, the p24delta(2) mutations prevented the Golgi localisation of the transgene products and caused a reduced rate of POMC cleavage, but did not lead to a reduction of the endogenous p24 proteins nor to aberrations in POMC glycosylation and sulphation. We conclude that p24delta(2) requires the presence of the COPI- and COPII-binding sites to allow proper POMC processing. Thus, the p24 proteins fulfil their role in secretory protein biosynthesis via COPI- or COPII-coated transport vesicles.
authors.affiliation: Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, and Nijmegen Centre for Molecular Life Sciences, 282 Department of Molecular Animal Physiology, Nijmegen, The Netherlands.
authors.forename: Jeroen R P M
authors.initials: JR
authors.lastname: Strating
authors.forename: Theo G M
authors.initials: TG
authors.lastname: Hafmans
authors.forename: Gerard J M
authors.initials: GJ
authors.lastname: Martens
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D022181:COP-Coated Vesicles / Q000378:metabolism*; D020755:Coat Protein Complex I / Q000378:metabolism*; D006031:Glycosylation; D052717:Melanotrophs / Q000166:cytology / Q000648:ultrastructure; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009928:Organ Specificity; D011333:Pro-Opiomelanocortin / Q000096:biosynthesis*; D011499:Protein Processing, Post-Translational; D013431:Sulfates / Q000378:metabolism; D019076:Transgenes; D029867:Xenopus Proteins / Q000737:chemistry / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism*
chemical_list: D020755:Coat Protein Complex I; D013431:Sulfates; D029867:Xenopus Proteins; D011333:Pro-Opiomelanocortin