title: The gamma/sigma1 and alpha/sigma2 hemicomplexes of clathrin adaptors AP-1 and AP-2 harbor the dileucine recognition site.
abstract: The clathrin adaptors AP-1 and AP-2 bind cargo proteins via two types of motifs: tyrosine-based Yxx phi and dileucine-based [DE]XXXL[LI]. Although it is well established that Yxx phi motifs bind to the mu subunits of AP-1 or AP-2, dileucine motifs have been reported to bind to either the mu or beta subunits of these adaptors as well as the gamma/sigma1 hemicomplex of AP-1. To clarify this controversy, the various subunits of AP-1 and AP-2 were expressed individually and in hemicomplex form in insect cells, and they were used in glutathione S-transferase pull-down assays to determine their binding properties. We report that the gamma/sigma1 or alpha/sigma2 hemicomplexes bound the dileucine-based motifs of several proteins quite strongly, whereas binding by the beta1/mu1 and beta2/mu2 hemicomplexes, and the individual beta or mu subunits, was extremely weak or undetectable. The gamma/sigma1 and alpha/sigma2 hemicomplexes displayed substantial differences in their preference for particular dileucine-based motifs. Most strikingly, an aspartate at position -4 compromised binding to the gamma/sigma1 hemicomplex, whereas minimally affecting binding to alpha/sigma2. There was an excellent correlation between binding to the alpha/sigma2 hemicomplex and in vivo internalization mediated by the dileucine-based sorting signals. These findings provide new insights into the trafficking mechanisms of D/EXXXL[LI]-mediated sorting signals.
authors.affiliation: Department of Internal Medicine and Pediatrics, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Balraj
authors.initials: B
authors.lastname: Doray
authors.forename: Intaek
authors.initials: I
authors.lastname: Lee
authors.forename: Jane
authors.initials: J
authors.lastname: Knisely
authors.forename: Guojun
authors.initials: G
authors.lastname: Bu
authors.forename: Stuart
authors.initials: S
authors.lastname: Kornfeld
mesh_terms: D033961:Adaptor Protein Complex 1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D033962:Adaptor Protein Complex 2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004151:Dipeptides / Q000737:chemistry; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D046912:Multiprotein Complexes / Q000737:chemistry; D021382:Protein Sorting Signals / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D033961:Adaptor Protein Complex 1; D033962:Adaptor Protein Complex 2; D004151:Dipeptides; D046912:Multiprotein Complexes; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; C038361:leucylleucine