BINDING STUDY OF METAL-IONS TO S100 PROTEIN - CA-43, MG-25, ZN-67 AND K-39 NMR

The interactions of the S100 protein (S100) with metal cations such as Ca2+, Mg2+, Zn2+ and K+ were studied by the metal n.m.r. spectroscopy. The line widths of Ca-43, Mg-25, Zn-67 and K-39 n.m.r. markedly increased by adding all S100s. A broad Ca-43 n.m.r. band of Ca2+-S100a solution was not affected by Zn2+ and K+, while it was greatly decreased by adding Mg2+. The Ca-43 n.m.r. spectra of Ca2+-S100a0 and -S100b solutions consisted of two slow-exchangeable signals which corresponded to Ca2+ bound to two environmentally different sites of the S100a0. These two Ca-43 n.m.r. signals were not affected by Zn2+ and K+. The line width of broad Mg-25 n.m.r. band of the Mg2+-S100 solution greatly decreased by adding Ca2+, while it did not change by adding Zn2+ and K+. Further, the addition of Ca2+, Mg2+ and K+ did not affect the line width of the Zn-67 n.m.r. of the Zn2+-S100 solutions. These findings suggest that: (1) Mg2+ binds to all S100s, and at least one of the Mg2+ binding sites of S100 molecule is the same as the Ca2+ binding site: (2) Zn2+ binds to S100s, although the binding site(s) is/are different from Ca2+ - or Mg2+-binding site(s), and the environment of Zn2+ nuclei will not change even though Ca2+ binds to S100s.