title: The crystal structure of metal-free human EF-hand protein S100A3 at 1.7-A resolution.
abstract: S100A3 is a unique member of the EF-hand superfamily of Ca(2+)-binding proteins. It binds Ca(2+) with poor affinity (K(d) = 4-35 mm) but Zn(2+) with exceptionally high affinity (K(d) = 4 nm). This high affinity for Zn(2+) is attributed to the unusual high Cys content of S100A3. The protein is highly expressed in fast proliferating hair root cells and astrocytoma pointing toward a function in cell cycle control. We determined the crystal structure of the protein at 1.7 A. The high resolution structure revealed a large distortion of the C-terminal canonical EF-hand, which most likely abolishes Ca(2+) binding. The crystal structure of S100A3 allows the prediction of one putative Zn(2+) binding site in the C terminus of each subunit of S100A3 involving Cys and His residues in the coordination of the metal ion. Zn(2+) binding induces a large conformational change in S100A3 perturbing the hydrophobic interface between two S100A3 subunits, as shown by size exclusion chromatography and CD spectroscopy.
authors.affiliation: Department of Pediatrics, Division of Clinical Chemistry and Biochemistry, Universität Zürich, Steinwiesstrasse 75, CH-8032 Zürich, Switzerland. gfritz@bioc.unizh.ch
authors.forename: Gunter
authors.initials: G
authors.lastname: Fritz
authors.forename: Peer R E
authors.initials: PR
authors.lastname: Mittl
authors.forename: Milan
authors.initials: M
authors.lastname: Vasak
authors.forename: Markus G
authors.initials: MG
authors.lastname: Grutter
authors.forename: Claus W
authors.initials: CW
authors.lastname: Heizmann
mesh_terms: D000595:Amino Acid Sequence; D000730:Androstadienes / Q000494:pharmacology; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry; D019281:Dimerization; D020832:EF Hand Motifs; D004926:Escherichia coli / Q000378:metabolism; D006639:Histidine / Q000737:chemistry; D006801:Humans; D006860:Hydrogen Bonding; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D009418:S100 Proteins; D015398:Signal Transduction; D000077191:Wortmannin; D015032:Zinc / Q000737:chemistry / Q000378:metabolism
chemical_list: D000730:Androstadienes; D002135:Calcium-Binding Proteins; D009418:S100 Proteins; C082356:S100A3 protein, human; D006639:Histidine; D015032:Zinc; D003545:Cysteine; D002118:Calcium; D000077191:Wortmannin