Molecular mechanism of APC/C activation by mitotic phosphorylation.
In eukaryotes, the anaphase-promoting complex (APC/C, also known as the cyclosome) regulates the ubiquitin-dependent proteolysis of specific cell-cycle proteins to coordinate chromosome segregation in mitosis and entry into the G1 phase. The catalytic activity of the APC/C and its ability to specify the destruction of particular proteins at different phases of the cell cycle are controlled by its interaction with two structurally related coactivator subunits, Cdc20 and Cdh1. Coactivators recognize substrate degrons, and enhance the affinity of the APC/C for its cognate E2 (refs 4-6). During mitosis, cyclin-dependent kinase (Cdk) and polo-like kinase (Plk) control Cdc20- and Cdh1-mediated activation of the APC/C. Hyperphosphorylation of APC/C subunits, notably Apc1 and Apc3, is required for Cdc20 to activate the APC/C, whereas phosphorylation of Cdh1 prevents its association with the APC/C. Since both coactivators associate with the APC/C through their common C-box and Ile-Arg tail motifs, the mechanism underlying this differential regulation is unclear, as is the role of specific APC/C phosphorylation sites. Here, using cryo-electron microscopy and biochemical analysis, we define the molecular basis of how phosphorylation of human APC/C allows for its control by Cdc20. An auto-inhibitory segment of Apc1 acts as a molecular switch that in apo unphosphorylated APC/C interacts with the C-box binding site and obstructs engagement of Cdc20. Phosphorylation of the auto-inhibitory segment displaces it from the C-box-binding site. Efficient phosphorylation of the auto-inhibitory segment, and thus relief of auto-inhibition, requires the recruitment of Cdk-cyclin in complex with a Cdk regulatory subunit (Cks) to a hyperphosphorylated loop of Apc3. We also find that the small-molecule inhibitor, tosyl-l-arginine methyl ester, preferentially suppresses APC/C(Cdc20) rather than APC/C(Cdh1), and interacts with the binding sites of both the C-box and Ile-Arg tail motifs. Our results reveal the mechanism for the regulation of mitotic APC/C by phosphorylation and provide a rationale for the development of selective inhibitors of this state.
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
Suyang
S
Zhang
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
Leifu
L
Chang
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
Claudio
C
Alfieri
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
Ziguo
Z
Zhang
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
Jing
J
Yang
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
Sarah
S
Maslen
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
Mark
M
Skehel
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
David
D
Barford
D020816:Amino Acid Motifs; D064173:Anaphase-Promoting Complex-Cyclosome / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D015703:Antigens, CD; D064189:Apc1 Subunit, Anaphase-Promoting Complex-Cyclosome / Q000737:chemistry / Q000378:metabolism; D064191:Apc3 Subunit, Anaphase-Promoting Complex-Cyclosome / Q000378:metabolism; D001051:Apoenzymes / Q000378:metabolism; D001665:Binding Sites; D015820:Cadherins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D064199:Cdc20 Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D020285:Cryoelectron Microscopy; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D008938:Mitosis; D008958:Models, Molecular; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D014106:Tosylarginine Methyl Ester / Q000494:pharmacology
D015703:Antigens, CD; D064189:Apc1 Subunit, Anaphase-Promoting Complex-Cyclosome; D064191:Apc3 Subunit, Anaphase-Promoting Complex-Cyclosome; D001051:Apoenzymes; C513384:CDH1 protein, human; D015820:Cadherins; D064199:Cdc20 Proteins; D016213:Cyclins; D010750:Phosphoproteins; C577488:CDC20 protein, human; D014106:Tosylarginine Methyl Ester; D064173:Anaphase-Promoting Complex-Cyclosome; D018844:Cyclin-Dependent Kinases