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Mol Biol Cell. 2016 Feb 1;27(3):588-98. doi: 10.1091/mbc.E15-09-0621. Epub 2015 Dec 10.

The alternate AP-1 adaptor subunit Apm2 interacts with the Mil1 regulatory protein and confers differential cargo sorting.

Author information

1
Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Vancouver, University of British Columbia, Vancouver, BC V5Z 4H4, Canada Department of Biochemistry and Molecular Biology and Department of Medical Genetics, Faculty of Medicine, University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
2
Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Vancouver, University of British Columbia, Vancouver, BC V5Z 4H4, Canada.
3
Department of Biology, Johns Hopkins University, Baltimore, MD 21218-2685.
4
Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Vancouver, University of British Columbia, Vancouver, BC V5Z 4H4, Canada Department of Biochemistry and Molecular Biology and Department of Medical Genetics, Faculty of Medicine, University of British Columbia, Vancouver, BC V6T 1Z3, Canada conibear@cmmt.ubc.ca.

Abstract

Heterotetrameric adaptor protein complexes are important mediators of cargo protein sorting in clathrin-coated vesicles. The cell type-specific expression of alternate μ chains creates distinct forms of AP-1 with altered cargo sorting, but how these subunits confer differential function is unclear. Whereas some studies suggest the μ subunits specify localization to different cellular compartments, others find that the two forms of AP-1 are present in the same vesicle but recognize different cargo. Yeast have two forms of AP-1, which differ only in the μ chain. Here we show that the variant μ chain Apm2 confers distinct cargo-sorting functions. Loss of Apm2, but not of Apm1, increases cell surface levels of the v-SNARE Snc1. However, Apm2 is unable to replace Apm1 in sorting Chs3, which requires a dileucine motif recognized by the γ/σ subunits common to both complexes. Apm2 and Apm1 colocalize at Golgi/early endosomes, suggesting that they do not associate with distinct compartments. We identified a novel, conserved regulatory protein that is required for Apm2-dependent sorting events. Mil1 is a predicted lipase that binds Apm2 but not Apm1 and contributes to its membrane recruitment. Interactions with specific regulatory factors may provide a general mechanism to diversify the functional repertoire of clathrin adaptor complexes.

PMID:
26658609
PMCID:
PMC4751606
DOI:
10.1091/mbc.E15-09-0621
[Indexed for MEDLINE]
Free PMC Article

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