title: New insights into the interaction of centrin with Sfi1.
abstract: Centrin binds to Rad4(XPC) and Sfi1 through the hydrophobic motif W(1)xxL(4)xxxL(8) in the opposite orientation. Rad4 has one motif, but Sfi1 has approximately 20 repeats, each of which interacts with a centrin molecule. To investigate the parameters involved in centrin binding, we purified a ScSfi1 domain containing 6 repeats complexed with either yeast centrin Cdc31 or human centrin 1. The present study was performed using mutagenesis of centrin and of Sfi1 residues involved in centrin binding and the stability of the centrin-centrin complexes was assessed using thermal denaturation and CD. Calcium stabilized these complexes, as indicated by the Tm increases measured by circular dichroism. The complexes, which were composed of Sfi1 variants and yeast centrin, were analysed in the presence of EDTA. The replacement of W with F within the repeat region yielded a functional repeat (Tm 45°C). The replacement of W with A in two adjacent Sfi1 repeats reduced the thermal stability of the Sfi1-centrin complexes (40°C). We analysed three HsCen1 variants that were homologous to the yeast mutants and induced cell cycle arrest during the G2/M transition. The HsCen1 variants E105K and F113L reduced the thermal stability (50°C, 50°C) of the ScSfi1-HsCen1 complexes; in contrast, the A109T variant exhibited no change in thermal stability relative to the wild-type (60°C). Conversely to ScCdc31, there were no apparent centrin-centrin interactions with wild-type HsCen1, but they did occur for the S170D mutation that mimics PKA phosphorylation at the S170 residue.
authors.affiliation: Institut Curie-Centre de Recherche, F-91405 Orsay Cédex, France; Institut National de la Santé et de la Recherche Médicale (INSERM) U759, F-91405 Orsay Cédex, France.
authors.forename: Juan
authors.initials: J
authors.lastname: Martinez-Sanz
authors.affiliation: Institut Curie-Centre de Recherche, F-91405 Orsay Cédex, France; Institut National de la Santé et de la Recherche Médicale (INSERM) U759, F-91405 Orsay Cédex, France. Electronic address: liliane.assairi@orange.fr.
authors.forename: Liliane
authors.initials: L
authors.lastname: Assairi
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D059447:Cell Cycle Checkpoints; D018797:Cell Cycle Proteins / Q000737:chemistry*; D004492:Edetic Acid / Q000494:pharmacology; D008969:Molecular Sequence Data; D010766:Phosphorylation; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000737:chemistry*
chemical_list: D018797:Cell Cycle Proteins; C545864:Sfi1 protein, human; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D004492:Edetic Acid
keywords: Binding; Centrin; Circular dichroism; Isothermal titration calorimetry; Sfi1