title: Beta3A-adaptin, a subunit of the adaptor-like complex AP-3.
abstract: Recent studies have described a widely expressed adaptor-like complex, named AP-3, which is likely involved in protein sorting in exocytic/endocytic pathways. The AP-3 complex is composed of four distinct subunits. Here, we report the identification of one of the subunits of this complex, which we call beta3A-adaptin. The predicted amino acid sequence of beta3A-adaptin reveals that the protein is closely related to the neuron-specific protein beta-NAP (61% overall identity) and more distantly related to the beta1- and beta2-adaptin subunits of the clathrin-associated adaptor complexes AP-1 and AP-2, respectively. Sequence comparisons also suggest that beta3A-adaptin has a domain organization similar to beta-NAP and to beta1- and beta2-adaptins. beta3A-adaptin is expressed in all tissues and cells examined. Co-purification and co-precipitation analyses demonstrate that beta3A-adaptin corresponds to the approximately 140-kDa subunit of the ubiquitous AP-3 complex, the other subunits being delta-adaptin, p47A (now called mu3A) and sigma3 (A or B). beta3A-adaptin is phosphorylated on serine residues in vivo while the other subunits of the complex are not detectably phosphorylated. beta3A-adaptin is not present in significant amounts in clathrin-coated vesicles. The characteristics of beta3A-adaptin reported here lend support to the idea that AP-3 is a structural and functional homolog of the clathrin-associated adaptors AP-1 and AP-2.
authors.affiliation: Cell Biology and Metabolism Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: E C
authors.initials: EC
authors.lastname: Dell'Angelica
authors.forename: C E
authors.initials: CE
authors.lastname: Ooi
authors.forename: J S
authors.initials: JS
authors.lastname: Bonifacino
mesh_terms: D033961:Adaptor Protein Complex 1; D033963:Adaptor Protein Complex 3; D033966:Adaptor Protein Complex beta Subunits; D000595:Amino Acid Sequence; D002966:Clathrin / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism
chemical_list: D033961:Adaptor Protein Complex 1; D033963:Adaptor Protein Complex 3; D033966:Adaptor Protein Complex beta Subunits; D002966:Clathrin; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D014157:Transcription Factors