Subunit of novel type of clathrin- or non-clathrin-associated protein coat involved in targeting proteins from the trans-Golgi network (TGN) to the endosomal-lysosomal system.
J. Biol. Chem. 274, 7278-7285 (1999)[PubMed:10066790]
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 beta and sigma subunits named beta4 and sigma4, respectively. An antibody to beta4 recognized in human cells an approximately 83-kDa polypeptide that exists in both soluble and membrane-associated forms. Gel filtration, sedimentation velocity, and immunoprecipitation experiments revealed that beta4 is a component of a multisubunit complex (AP-4) that also contains the sigma4 polypeptide and two additional adaptor subunit homologs named mu4 (mu-ARP2) and epsilon. 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.
The directed movement of proteins in a cell, including the movement of proteins between specific compartments or structures within a cell, such as organelles of a eukaryotic cell.
A cellular transport process in which transported substances are moved in membrane-bounded vesicles; transported substances are enclosed in the vesicle lumen or located in the vesicle membrane. The process begins with a step that directs a substance to the forming vesicle, and includes vesicle budding and coating. Vesicles are then targeted to, and fuse with, an acceptor membrane.
IEAInterPro 2 GO
Pathways
According to KEGG, this protein belongs to the following pathway:
Protein involved in the intracellular transport of proteins from one location to another. All proteins (except the ones synthesized in mitochondria and plastids) are synthesized on ribosomes in the cytosol. Most proteins remain in the cytosol. Proteins with a signal sequence either become plasma membrane components or are exported from the cell of origin.
Protein involved in the transport of a molecule (metabolite, protein, etc), a ion or an electron across cell membranes, inside the cell or in a tissue fluid.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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