S-100 protein, but not calmodulin, binds to the glial fibrillary acidic protein and inhibits its polymerization in a Ca(2+)-dependent manner.
S-100 protein, a Ca(2+)-binding protein of the EF-hand type, interacts with the glial fibrillary acidic protein (GFAP) in a Ca(2+)-dependent manner. The binding of S-100 protein to GFAP was investigated by fluorescence spectroscopy using acrylodan-S-100 protein and cross-linking experiments using the bifunctional cross-linker, disuccinimidyl suberate. The binding affinity was observed to be in the nanomolar range with a stoichiometry of 2 mol of GFAP/mol of S-100 protein (dimer). S-100 protein was found to inhibit the polymerization of GFAP in a dose- and Ca(2+)-dependent manner, with a half-maximal effect at an S-100 protein/GFAP molar ratio of 0.2 and maximal effect at a molar ratio of 0.5. Identical results were obtained irrespective of whether the unfractionated bovine brain S-100 protein mixture (S-100a plus S-100b), S-100ao, S-100a, or S-100b was used. S-100 protein was observed to be maximally effective as an inhibitor of GFAP polymerization at approximately 3 microM free Ca2+. Calmodulin neither bound to GFAP nor inhibited its polymerization. Altogether, the present results suggest that S-100 protein might be involved in the regulation of the state of assembly of glial filaments by binding to and sequestering unpolymerized GFAP.
Department of Experimental Medicine and Biochemical Sciences, University of Perugia, Italy.
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Bianchi
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Giambanco
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Donato
D015081:2-Naphthylamine / Q000031:analogs & derivatives; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000302:isolation & purification / Q000378:metabolism*; D002417:Cattle; D002852:Chromatography, Ion Exchange; D003432:Cross-Linking Reagents; D004591:Electrophoresis, Polyacrylamide Gel; D005456:Fluorescent Dyes; D005904:Glial Fibrillary Acidic Protein / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D011485:Protein Binding; D009418:S100 Proteins / Q000302:isolation & purification / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013388:Succinimides
D002147:Calmodulin; D003432:Cross-Linking Reagents; D005456:Fluorescent Dyes; D005904:Glial Fibrillary Acidic Protein; D046911:Macromolecular Substances; D009418:S100 Proteins; D013388:Succinimides; C038518:acrylodan; D015081:2-Naphthylamine; D002118:Calcium; C019358:disuccinimidyl suberate