Ca(II) and Zn(II) synergistically modulate the structure and self‐assembly of Calgranulin C (S100A12)

Abstract

S100A12 is a member of the Ca(II) binding S100 family of proteins that functions within the human innate immune system. As a metal‐chelator, S100A12 binds both Ca(II) and Zn(II) at structurally distinct sites. Ca(II) binding enhances the Zn(II) binding affinity and the mechanism of the mode of action of Ca(II) is not fully understood. Here, using solution and solid state NMR spectroscopy, we have conducted structural characterization of S100A12 upon Ca(II) and Zn(II) binding. We demonstrate that distinct conformational changes are introduced in helix II and the hinge domain of the protein upon Zn(II) binding to Ca(II)‐S100A12, suggesting that both ions modulate the structure of S100A12. Moreover, Ca(II)‐S100A12 exhibits a broader pH range for Zn(II) binding compared to the apo protein by restricting conformational changes to Zn(II) binding residue, D25. In conclusion, our results indicate that Ca(II) stabilizes Zn(II) binding affinity by modulating structural changes. These findings will be of value for understanding of the nutrient‐sequestration effect of neutrophils and the interaction between the S100A12 and other receptors such as receptor for advanced glycation endproducts (RAGE) and toll‐like receptor 4 (TLR).Support or Funding InformationThis work was supported by the City University of New York startup funds, the National Institutes of Health (R15GM131338) and PSC CUNY award (62234‐00 50) to Rupal Gupta. NMR data presented herein were collected (in part) at the City University of New York’s Advanced Science Research Center (CUNY ASRC) Biomolecular NMR Facility.MAS NMR spectra of apo and Zn2+‐S100A12. a) Left: DARR (14.1 T) and NCACX (16.4 T) 2D spectra apo S100A12 with resonance assignments; Right: strip plots from CBCACONH (blue) and HNCACB (orange) solution NMR spectra for residues T26‐S28. Signals belonging to an assigned residue in MAS and solution spectra are connected with the same color; b) overlay of Zn2+‐(orange) and apo‐(blue) S100A12 DARR spectra acquired at 14.1 T and; c)–e) expansions of b) with assignments of the perturbed residues.Figure 1