Nuclear magnetic resonance studies of calcyclin and annexin XI.

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Ca^<2+>-binding proteins is classified into major 3 groups based on structure of the Ca^<2+>-binding domain, 1) EF-hand proteins, 2) annexins, 3) C2-domain proteins. This study was mainly aimed at the elucidation of three-dimensional structure of calcyclin, a member of S100 family with 2 EF-hands and annexin XI which is a ligand of calcyclin with NMR spectroscopy. The three dimensional structure of calcyclin has been determined in solution in the apo state by NMR spectroscopy and a computational strategy that incorporates a systematic docking protocol. This structure reveals a symmetric homodimeric fold that is unique among Ca^<2+>-binding proteins. Dimerization is mediated by hydrophobic contacts from several highly conserved residues, which suggests that the dimer fold identified for calcyclin will serve as a structural paradigm for the S100 subfamily of Ca^<2+>-binding proteins.The subcellular localization of annexin XI is, unique among the family, mainly in a uncleus of cells such … More as COS-7 and is altered by phosphorylation. In this study, it was revealed that annexin XI localized in a nucleus by the regulatory domain as nuclear localization signal, and the localization is regulated depending on developmental and growth stages, and cell types, and annexin XI isoforms generated by alternative splicing in the N-terminal regulatory domain differed in subcellular localization.We indentified the calcyclin binding domain on annexin XI with annexin XI-GST fusion proteins. This results indicated that calcyclin bound in the region from Gln49 to Thr62. Chou-Fasman analysis of the binding domain suggest a highly probability for a-helical formation with hydrophobic residues aligning onto one side of a theoretical amphipathic helix. It was suggested that the annexin XI hydrophobic face was the binding site for calcyclin. We synthesized the peptide containing the calcyclin binding site of annexin XI,which could bind to calcyclin. We have been analyzed the three-dimensional structure of the complex of calcyclin and the calcyclin binding peptide of annexin XI with NMR spectroscopy. These results obtained in this study contribute to the studies of not only the structure analysis of Ca^<2+>-binding proteins but also the protein-protein interaction in other field. Less