title: Dimerization Mediated by a Divergent Forkhead-associated Domain Is Essential for the DNA Damage and Spindle Functions of Fission Yeast Mdb1.
abstract: MDC1 is a key factor of DNA damage response in mammalian cells. It possesses two phospho-binding domains. In its C terminus, a tandem BRCA1 C-terminal domain binds phosphorylated histone H2AX, and in its N terminus, a forkhead-associated (FHA) domain mediates a phosphorylation-enhanced homodimerization. The FHA domain of the Drosophila homolog of MDC1, MU2, also forms a homodimer but utilizes a different dimer interface. The functional importance of the dimerization of MDC1 family proteins is uncertain. In the fission yeast Schizosaccharomyces pombe, a protein sharing homology with MDC1 in the tandem BRCA1 C-terminal domain, Mdb1, regulates DNA damage response and mitotic spindle functions. Here, we report the crystal structure of the N-terminal 91 amino acids of Mdb1. Despite a lack of obvious sequence conservation to the FHA domain of MDC1, this region of Mdb1 adopts an FHA-like fold and is therefore termed Mdb1-FHA. Unlike canonical FHA domains, Mdb1-FHA lacks all the conserved phospho-binding residues. It forms a stable homodimer through an interface distinct from those of MDC1 and MU2. Mdb1-FHA is important for the localization of Mdb1 to DNA damage sites and the spindle midzone, contributes to the roles of Mdb1 in cellular responses to genotoxins and an antimicrotubule drug, and promotes in vitro binding of Mdb1 to a phospho-H2A peptide. The defects caused by the loss of Mdb1-FHA can be rescued by fusion with either of two heterologous dimerization domains, suggesting that the main function of Mdb1-FHA is mediating dimerization. Our data support that FHA-mediated dimerization is conserved for MDC1 family proteins.
authors.affiliation: National Institute of Biological Sciences, Beijing 102206, China.
authors.forename: Shukun
authors.initials: S
authors.lastname: Luo
authors.affiliation: National Institute of Biological Sciences, Beijing 102206, China.
authors.forename: Xiaoran
authors.initials: X
authors.lastname: Xin
authors.affiliation: National Institute of Biological Sciences, Beijing 102206, China. Electronic address: dulilin@nibs.ac.cn.
authors.forename: Li-Lin
authors.initials: LL
authors.lastname: Du
authors.affiliation: National Institute of Biological Sciences, Beijing 102206, China; Key Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China. Electronic address: yekeqiong@nibs.ac.cn.
authors.forename: Keqiong
authors.initials: K
authors.lastname: Ye
authors.affiliation: National Institute of Biological Sciences, Beijing 102206, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Wei
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D006657:Histones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008938:Mitosis / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D017510:Protein Folding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D012568:Schizosaccharomyces / Q000235:genetics* / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction; D008941:Spindle Apparatus / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D040681:Structural Homology, Protein; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D006657:Histones; C413163:MDC1 protein, human; C121266:MU2 protein, Drosophila; C000598595:Mdb1 protein, S pombe; D009687:Nuclear Proteins; D010750:Phosphoproteins; D029702:Schizosaccharomyces pombe Proteins; D015534:Trans-Activators
keywords: DNA damage response; H2A histone family, member X (H2AFX); MDC1; Mdb1; Schizosaccharomyces pombe; crystal structure; dimerization; forkhead-associated domain (FHA domain); mitotic spindle; protein-protein interaction