Crystal structure of a beta-catenin/APC complex reveals a critical role for APC phosphorylation in APC function.
The tumor suppressor adenomatous polyposis coli (APC) plays a critical role in the turnover of cytosolic beta-catenin, the key effector of the canonical Wnt signaling pathway. APC contains seven 20 amino acid (20 aa) beta-catenin binding repeats that are required for beta-catenin turnover. We have determined the crystal structure of beta-catenin in complex with a phosphorylated APC fragment containing two 20 aa repeats. Surprisingly, one single phosphorylated 20 aa repeat, together with its flanking regions, covers the entire structural groove of beta-catenin and may thus compete for beta-catenin binding with all other beta-catenin armadillo repeat partners. Our biochemical studies show that phosphorylation of the APC 20 aa repeats increases the affinity of the repeats for beta-catenin by 300- to 500-fold and the phosphorylated 20 aa repeats prevent beta-catenin binding to Tcf. Our work suggests that the phosphorylation of the APC 20 aa repeats could be a critical switch for APC function.
Department of Biological Structure, University of Washington, Seattle, WA 98195, USA.
Yi
Y
Xing
Wilson K
WK
Clements
Isolde
I
Le Trong
Thomas R
TR
Hinds
Ronald
R
Stenkamp
David
D
Kimelman
Wenqing
W
Xu
D025601:Adenomatous Polyposis Coli Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012091:Repetitive Sequences, Nucleic Acid; D016415:Sequence Alignment; D015534:Trans-Activators / Q000737:chemistry* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D051176:beta Catenin
D025601:Adenomatous Polyposis Coli Protein; C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D051176:beta Catenin