The structure of calcyclin reveals a novel homodimeric fold for S100 Ca(2+)-binding proteins

The S100 calcium-binding proteins are implicated as effectors in calcium-mediated signal transduction pathways. The three-dimensional structure of the S100 protein 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 calcium-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 calcium-binding proteins.