title: Solution structure of zinc- and calcium-bound rat S100B as determined by nuclear magnetic resonance spectroscopy.
abstract: The EF-hand calcium-binding protein S100B also binds one zinc ion per subunit with a relatively high affinity (K(d) approximately 90 nM) [Wilder et al., (2003) Biochemistry 42, 13410-13421]. In this study, the structural characterization of zinc binding to calcium-loaded S100B was examined using high-resolution NMR techniques, including structural characterization of this complex in solution at atomic resolution. As with other S100 protein structures, the quaternary structure of Zn(2+)-Ca(2+)-bound S100B was found to be dimeric with helices H1, H1', H4, and H4' forming an X-type four-helix bundle at the dimer interface. NMR data together with mutational analyses are consistent with Zn(2+) coordination arising from His-15 and His-25 of one S100B subunit and from His-85 and Glu-89 of the other subunit. The addition of Zn(2+) was also found to extend helices H4 and H4' three to four residues similar to what was previously observed with the binding of target proteins to S100B. Furthermore, a kink in helix 4 was observed in Zn(2+)-Ca(2+)-bound S100B that is not in Ca(2+)-bound S100B. These structural changes upon Zn(2+)-binding could explain the 5-fold increase in affinity that Zn(2+)-Ca(2+)-bound S100B has for peptide targets such as the TRTK peptide versus Ca(2+)-bound S100B. There are also changes in the relative positioning of the two EF-hand calcium-binding domains and the respective helices comprising these EF-hands. Changes in conformation such as these could contribute to the order of magnitude higher affinity that S100B has for calcium in the presence of Zn(2+).
authors.affiliation: Molecular and Cell Biology Program, University of Maryland School of Medicine, 108 North Greene Street, Baltimore, Maryland 21201, USA.
authors.forename: Paul T
authors.initials: PT
authors.lastname: Wilder
authors.forename: Kristen M
authors.initials: KM
authors.lastname: Varney
authors.forename: Michele B
authors.initials: MB
authors.lastname: Weiss
authors.forename: Rossitza K
authors.initials: RK
authors.lastname: Gitti
authors.forename: David J
authors.initials: DJ
authors.lastname: Weber
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D066298:In Vitro Techniques; D008024:Ligands; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009414:Nerve Growth Factors; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012996:Solutions; D015032:Zinc / Q000378:metabolism
chemical_list: D008024:Ligands; D009414:Nerve Growth Factors; D021122:Protein Subunits; D011994:Recombinant Proteins; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins; C579158:S100b protein, rat; D012996:Solutions; D015032:Zinc; D002118:Calcium