title: The crystal structure at 2A resolution of the Ca2+ -binding protein S100P.
abstract: S100P is a small calcium-binding protein of the S100 EF-hand-containing family of proteins. Elevated levels of its mRNA are reported to be associated with the progression to hormone independence and metastasis of prostate cancer and to be associated with loss of senescence in human breast epithelial cells in vitro. The first structure of human recombinant S100P in calcium-bound form is now reported at 2.0A resolution by X-ray diffraction. A flexible linker connects the two EF-hand motifs. The protein exists as a homodimer formed by non-covalent interactions between large hydrophobic areas on monomeric S100P. Experiments with an optical biosensor to study binding parameters of the S100P monomer interaction showed that the association rate constant was faster in the presence of calcium than in their absence, whereas the dissociation rate constant was independent of calcium. The K(d) values were 64(+/-24)nM and 2.5(+/-0.8) microM in the presence and in the absence of calcium ions, respectively. Dimerization of S100P is demonstrated in vivo using the yeast two-hybrid system. The effect of mutation of specific amino acids suggests that dimerization in vivo can be affected by amino acids on the dimer interface and in the hydrophobic core.
authors.affiliation: Laboratory of Structural Biology & MOE Laboratory of Protein Science, School of Life Science and Engineering, Tsinghua University, Beijing 100084, People's Republic of China.
authors.forename: Hongmei
authors.initials: H
authors.lastname: Zhang
authors.forename: Guozheng
authors.initials: G
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Ding
authors.forename: Zhilong
authors.initials: Z
authors.lastname: Wang
authors.forename: Roger
authors.initials: R
authors.lastname: Barraclough
authors.forename: Philip S
authors.initials: PS
authors.lastname: Rudland
authors.forename: David G
authors.initials: DG
authors.lastname: Fernig
authors.forename: Zihe
authors.initials: Z
authors.lastname: Rao
mesh_terms: D000595:Amino Acid Sequence; D015374:Biosensing Techniques; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D019281:Dimerization; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D009363:Neoplasm Proteins; D055095:Optics and Photonics; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009418:S100 Proteins / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D002135:Calcium-Binding Proteins; D009363:Neoplasm Proteins; D011994:Recombinant Proteins; D009418:S100 Proteins; C103003:S100P protein, human