Solution structure of zinc- and calcium-bound rat S100B as determined by nuclear magnetic resonance spectroscopy.

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TitleSolution structure of zinc- and calcium-bound rat S100B as determined by nuclear magnetic resonance spectroscopy.
Publication TypeJournal Article
Year of Publication2005
AuthorsWilder, PT, Varney, KM, Weiss, MB, Gitti, RK, Weber, DJ
Date Published2005 Apr 19
KeywordsAnimals, Binding Sites, Calcium, Ligands, Models, Molecular, Mutagenesis, Site-Directed, Nerve Growth Factors, Nuclear Magnetic Resonance, Biomolecular, Protein Binding, Protein Conformation, Protein Structure, Quaternary, Protein Subunits, Rats, Recombinant Proteins, S100 Proteins, Solutions, Zinc

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+).

Alternate JournalBiochemistry
PubMed ID15823027
Grant ListGM58888 / GM / NIGMS NIH HHS / United States