Structural and ion-binding properties of an S100b protein mixed disulfide: comparison with the reappraised native S100b protein properties.
S100b protein, chemically modified by thioethanol groups (linked via disulfide bonds to two out of four Cys per dimer) was largely similar to reduced native S100b protein in its overall structure and differed only by small modifications extending, however, to the whole protein structure. Studies combining direct Ca2+ binding and associated conformational changes revealed that this chemical modification markedly increased the Ca2(+)-binding affinities (especially in the presence of physiological concentrations of K+ and Mg2+) and introduced a strong positive cooperativity. Different binding models are discussed and it emerges that in both proteins the Ca2(+)-binding sites are not equivalent and probably interact. Like the reduced protein, chemically modified S100b protein binds four Zn2+ ions in two classes of sites (of high and low affinities). Whereas the overall Zn2+ affinity was only slightly decreased, the binding sequence was probably reversed by the introduction of thioethanol groups. Moreover, in the presence of zinc, the Ca2+ affinities were higher and even identical, in both proteins.
Mely
Y
Y
Université Louis Pasteur, UA CNRS 491, Faculté de Pharmacie de Strasbourg, Illkirch, France.
Gerard
D
D
D002118:Calcium / Q000378:metabolism*; D004220:Disulfides; D005453:Fluorescence; D008274:Magnesium / Q000378:metabolism; D009414:Nerve Growth Factors; D011487:Protein Conformation; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D014443:Tyrosine; D015032:Zinc / Q000378:metabolism
D004220:Disulfides; D009414:Nerve Growth Factors; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins; D014443:Tyrosine; D008274:Magnesium; D015032:Zinc; D002118:Calcium