2 research outputs found
Copper Binding Affinity of S100A13, a Key Component of the FGF-1 Nonclassical Copper-Dependent Release Complex
S100A13 is a member of the S100 protein family that is involved in the copper-dependent nonclassical secretion of signal peptideless proteins fibroblast growth factor 1 and interleukin 1α. In this study, we investigate the effects of interplay of Cu(2+) and Ca(2+) on the structure of S100A13 using a variety of biophysical techniques, including multi-dimensional NMR spectroscopy. Results of the isothermal titration calorimetry experiments show that S100A13 can bind independently to both Ca(2+) and Cu(2+) with almost equal affinity (K(d) in the micromolar range). Terbium binding and isothermal titration calorimetry data reveal that two atoms of Cu(2+)/Ca(2+) bind per subunit of S100A13. Results of the thermal denaturation experiments monitored by far-ultraviolet circular dichroism, limited trypsin digestion, and hydrogen-deuterium exchange (using (1)H-(15)N heteronuclear single quantum coherence spectra) reveal that Ca(2+) and Cu(2+) have opposite effects on the stability of S100A13. Binding of Ca(2+) stabilizes the protein, but the stability of the protein is observed to decrease upon binding to Cu(2+). (1)H-(15)N chemical shift perturbation experiments indicate that S100A13 can bind simultaneously to both Ca(2+) and Cu(2+) and the binding of the metal ions is not mutually exclusive. The results of this study suggest that the Cu(2+)-binding affinity of S100A13 is important for the formation of the FGF-1 homodimer and the subsequent secretion of the signal peptideless growth factor through the nonclassical release pathway