title: Structural basis for cell cycle checkpoint control by the BRCA1-CtIP complex.
abstract: The breast and ovarian tumor suppressor BRCA1 has important functions in cell cycle checkpoint control and DNA repair. Two tandem BRCA1 C-terminal (BRCT) domains are essential for the tumor suppression activity of BRCA1 and interact in a phosphorylation-dependent manner with proteins involved in DNA damage-induced checkpoint control, including the DNA helicase BACH1 and the CtBP-interacting protein (CtIP). The crystal structure of the BRCA1 BRCT repeats bound to the PTRVSpSPVFGAT phosphopeptide corresponding to residues 322-333 of human CtIP was determined at 2.5 A resolution. The peptide binds to a cleft formed by the interface of the two BRCTs in a two-pronged manner, with phospho-Ser327 and Phe330 anchoring the peptide through extensive contacts with BRCA1 residues. Several hydrogen bonds and salt bridges that stabilize the BRCA1-BACH1 complex are missing in the BRCA1-CtIP interaction, offering a structural basis for the approximately 5-fold lower affinity of BRCA1 for CtIP compared to that of BACH1, as determined by isothermal titration calorimetry. Importantly, the side chain of Arg1775 in the cancer-associated BRCA1 mutation M1775R sterically clashes with the phenyl ring of CtIP Phe330, disrupting the BRCA1-CtIP interaction. These results provide new insights into the molecular mechanisms underlying the dynamic selection of target proteins involved in DNA repair and cell cycle control by BRCA1 and reveal how certain cancer-associated mutations affect these interactions.
authors.affiliation: Molecular Medicine Laboratory and Macromolecular Crystallography Unit, Division of Experimental Medicine, Harvard Institutes of Medicine, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Ashok K
authors.initials: AK
authors.lastname: Varma
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Brown
authors.forename: Gabriel
authors.initials: G
authors.lastname: Birrane
authors.forename: John A A
authors.initials: JA
authors.lastname: Ladias
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D019313:BRCA1 Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D050976:Basic-Leucine Zipper Transcription Factors; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism; D002151:Calorimetry; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle; D018360:Crystallography, X-Ray; D004249:DNA Damage; D004260:DNA Repair; D004706:Endodeoxyribonucleases; D051856:Fanconi Anemia Complementation Group Proteins; D005260:Female; D006801:Humans; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D017354:Point Mutation; D011485:Protein Binding / Q000235:genetics; D020836:Protein Structure, Quaternary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D017186:Titrimetry; D014157:Transcription Factors / Q000378:metabolism
chemical_list: C102108:BACH1 protein, human; D019313:BRCA1 Protein; D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D051856:Fanconi Anemia Complementation Group Proteins; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; D014157:Transcription Factors; D004706:Endodeoxyribonucleases; C410741:RBBP8 protein, human