title: Structure of an APC3-APC16 complex: insights into assembly of the anaphase-promoting complex/cyclosome.
abstract: The anaphase-promoting complex/cyclosome (APC/C) is a massive E3 ligase that controls mitosis by catalyzing ubiquitination of key cell cycle regulatory proteins. The APC/C assembly contains two subcomplexes: the "Platform" centers around a cullin-RING-like E3 ligase catalytic core; the "Arc Lamp" is a hub that mediates transient association with regulators and ubiquitination substrates. The Arc Lamp contains the small subunits APC16, CDC26, and APC13, and tetratricopeptide repeat (TPR) proteins (APC7, APC3, APC6, and APC8) that homodimerize and stack with quasi-2-fold symmetry. Within the APC/C complex, APC3 serves as center for regulation. APC3's TPR motifs recruit substrate-binding coactivators, CDC20 and CDH1, via their C-terminal conserved Ile-Arg (IR) tail sequences. Human APC3 also binds APC16 and APC7 and contains a >200-residue loop that is heavily phosphorylated during mitosis, although the basis for APC3 interactions and whether loop phosphorylation is required for ubiquitination are unclear. Here, we map the basis for human APC3 assembly with APC16 and APC7, report crystal structures of APC3Δloop alone and in complex with the C-terminal domain of APC16, and test roles of APC3's loop and IR tail binding surfaces in APC/C-catalyzed ubiquitination. The structures show how one APC16 binds asymmetrically to the symmetric APC3 dimer and, together with biochemistry and prior data, explain how APC16 recruits APC7 to APC3, show how APC3's C-terminal domain is rearranged in the full APC/C assembly, and visualize residues in the IR tail binding cleft important for coactivator-dependent ubiquitination. Overall, the results provide insights into assembly, regulation, and interactions of TPR proteins and the APC/C.
authors.affiliation: Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
authors.forename: Masaya
authors.initials: M
authors.lastname: Yamaguchi
authors.affiliation: Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
authors.forename: Shanshan
authors.initials: S
authors.lastname: Yu
authors.affiliation: Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), 1030 Vienna, Austria.
authors.forename: Renping
authors.initials: R
authors.lastname: Qiao
authors.affiliation: Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), 1030 Vienna, Austria.
authors.forename: Florian
authors.initials: F
authors.lastname: Weissmann
authors.affiliation: Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
authors.forename: Darcie J
authors.initials: DJ
authors.lastname: Miller
authors.affiliation: Howard Hughes Medical Institute, St. Jude Children's Research Hospital, Memphis, TN 38105 USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: VanderLinden
authors.affiliation: Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Brown
authors.affiliation: Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
authors.forename: Jeremiah J
authors.initials: JJ
authors.lastname: Frye
authors.affiliation: Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), 1030 Vienna, Austria.
authors.forename: Jan-Michael
authors.initials: JM
authors.lastname: Peters
authors.affiliation: Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA; Howard Hughes Medical Institute, St. Jude Children's Research Hospital, Memphis, TN 38105 USA. Electronic address: Brenda.Schulman@stjude.org.
authors.forename: Brenda A
authors.initials: BA
authors.lastname: Schulman
mesh_terms: D000595:Amino Acid Sequence; D064191:Apc3 Subunit, Anaphase-Promoting Complex-Cyclosome / Q000737:chemistry* / Q000378:metabolism*; D064195:Apc7 Subunit, Anaphase-Promoting Complex-Cyclosome / Q000737:chemistry / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D018360:Crystallography, X-Ray; D006801:Humans; D008958:Models, Molecular; D011487:Protein Conformation; D060066:Protein Interaction Maps; D055503:Protein Multimerization; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism
chemical_list: C539689:ANAPC16 protein, human; C577399:ANAPC7 protein, human; D064191:Apc3 Subunit, Anaphase-Promoting Complex-Cyclosome; D064195:Apc7 Subunit, Anaphase-Promoting Complex-Cyclosome; C577366:CDC27 protein, human; D018797:Cell Cycle Proteins; D011506:Proteins; D044767:Ubiquitin-Protein Ligases
keywords: TPR; anaphase-promoting complex/cyclosome; cell cycle; protein assembly; ubiquitin E3 ligase