AP-4, a Novel Protein Complex Related to Clathrin Adaptors*
- From the Cell Biology and Metabolism Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892
Abstract
Here we report the identification and characterization of AP-4, a novel protein complex related to the heterotetrameric AP-1, AP-2, and AP-3 adaptors that mediate protein sorting in the endocytic and late secretory pathways. The key to the identification of this complex was the cloning and sequencing of two widely expressed, mammalian cDNAs encoding new homologs of the adaptor β and ς subunits named β4 and ς4, respectively. An antibody to β4 recognized in human cells an ∼83-kDa polypeptide that exists in both soluble and membrane-associated forms. Gel filtration, sedimentation velocity, and immunoprecipitation experiments revealed that β4 is a component of a multisubunit complex (AP-4) that also contains the ς4 polypeptide and two additional adaptor subunit homologs named μ4 (μ-ARP2) and ε. Immunofluorescence analyses showed that AP-4 is associated with the trans-Golgi network or an adjacent structure and that this association is sensitive to the drug brefeldin A. We propose that, like the related AP-1, AP-2, and AP-3 complexes, AP-4 plays a role in signal-mediated trafficking of integral membrane proteins in mammalian cells.
Footnotes
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↵* The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) AF092093 and AF092094.
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↵‡ Supported by a National Research Council Research Associateship.
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↵§ To whom correspondence should be addressed: CBMB, NICHD, National Institutes of Health, Bldg. 18T, Rm. 101, Bethesda, MD 20892. Tel.: 301-496-6368; Fax: 301-402-0078; E-mail: juan{at}helix.nih.gov.
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↵2 E. C. Dell’Angelica, and J. S. Bonifacino, unpublished results.
- Abbreviations:
- AP
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adaptor protein
- BSA
-
bovine serum albumin
- EST
-
expressed sequence tag
- GST
-
glutathione S-transferase
- kb
-
kilobase pair(s)
- PAGE
-
polyacrylamide gel electrophoresis
- PBS
-
phosphate-buffered saline
- PCR
-
polymerase chain reaction
- RACE
-
rapid amplification of cDNA ends
- TGN
-
trans-Golgi network
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- Received November 2, 1998.
- Revision received December 11, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
