Interactions of S100 Proteins with Proteins Kinase Substrates. Biological Implication
S-100 proteins are a group of low molecular weight (10 kDa) acidic proteins highly concentrated in brain tissues (for a recent review see Kligman and Hild, 1988). S100 proteins purified from bovine brain, are a mixture of hetero- and homodimer of two types of subunit, α and ß with different amino acid composition (Isobe et al., 1977). The amino acid sequence of the α and ß subunits revealed the structural relationship of S100 with the calcium binding proteins of the EF-hand type (Isobe and Okuyama, 1978). Both subunits have one 30-residue putative EF-hand calcium binding domain (site I) in the N-terminal part and one typical 28-residue domain (site II) in the C-terminal part. Calcium-binding studies on bovine brain S100αα and S100ßß (S100b) proteins confirmed the presence of two specific calcium-binding sites per subunits (Baudier et al., 1986a). The calcium binding sequence on the α and ß subunit have been studied by means of intrinsic fluorescence and absorption spectroscopy, binding of the Ca2+ analoge Tb3+ and H-NMR (in preparation), and showed that in both cases saturation of the typical Ca2+ -binding sites (site II) occured first followed by the binding of Ca2+ to the putative Ca2+ - binding site (site I). In the absence of monovalent cation the affinities of the typical sites II α and IIß range between 10–20 μM and those of the putative sites Iα and Iß range between 100–400 μM. In the presence of physiological intracellular KCl concentrations the S100 protein affinities for calcium drastically decrease to 500 μM -1 mM, which become probably not compatible with intracellular calcium concentrations. However, it has been shown that S100 protein affinities for calcium may also depend greatly on the quaternary and tertiary protein structures. Conformational effectors such as Zn2+ ions in the peculiar case of S100b, alkylation of Cys 85α or Cys 84ß, or interaction with target protein were proved to greatly increase the calcium binding affinities of sites II α and IIß in the range of .5 –10 μM and to decrease the antagonistic effect of KCl on calcium binding (Baudier et al., 1986a, 1986b, 1987a).
KeywordsS100 Protein Calcium Binding Bovine Brain Microtubule Assembly Paired Helical Filament
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- Baudier, J., Mochley-Rosen, D., Newton, A., Lee, S.H., Koshland, D.E., and Cole, R.D., 1987a, Comparison of S100b protein with calmodulin: interaction with melittin and microtubule-associated tau proteins and inhibition of phosphorylation of tau proteins by protein kinase C. Biochemistry. 26: 2886.PubMedCrossRefGoogle Scholar
- Baudier, J., and Cole, R.D., 1988b, Reinvestigation of the sulfhydryl reactivity in bovine brain S100b(ßß) protein and the microtubule-associated tau proteins. Ca2+ stimulates disulfide cross-linking between the S100b ß subunit and the microtubule-associated tau(2) protein. Biochemistry. 27: 2728.PubMedCrossRefGoogle Scholar
- Baudier, J., 1988, S100 proteins: Structure and calcium binding properties, in “Calcium and calcium binding proteins,” C. Gerday, R. Gilles, and L. Bolis, eds., Springer-Verlag, Berlin Heidelberg.Google Scholar
- Patel, J., and Kligman, D., 1988, Purification and characterization of an Mr 87,000 protein kinase C substrate from rat brain. J. Biol. Chem., 262:16686.Google Scholar
- Zimmer, D.B., and Van Eldik, L.J., 1987, Identification of a molecular target for the calcium-modulated protein S100: Fructose-1,6-biphosphate aldolase. J. Biol. Chem., 261:11424.Google Scholar