S-lOOb) on desmin assembly in vitro

0892-6638/96/0010-031 7/sQl .50. © FASEB 317 ABSTRACT: S-100a0, the aa isoform of a subfamily of Ca2 4-binding proteins of the EF-hand type expressed in cardiac and skeletal muscle cells, is reported to inhibit the assembly of the intermediate filament subunit desinin and to stimulate the disassembly of desmin intermediate filaments in the presence of micromolar levels of free Ca2 + These effects are dose-dependent with respect to the S-100a0 concentration and maximal at a desmiu/S1 00a0 (dimer) molar ratio of -2. Other members of the S-i 00 subfamily [S-iOOa (c43) and S-bOb (I3)] and the unfractionated mixture of S-iOOa plus S-iOOb produce qualitatively similar effects on desmin assembly, with a potency that depends on the fraction of 5i00ct subunit (the most potent) or S-100 subunit (the least potent) present in the S-100 isoforms tested. A binding stoichiometry of 2 mol of desmin/mol of S-iOOa0 (dimer) and an affinity in the submicromolar range are calculated. The S-100 subunit also interacts with desmin, but with a lower affinity compared with S-lOOa. By contrast, the S-iOO-like proteins calcyclin and ph neither interact with desmnin nor affect desmin assembly. The present data suggest that S-i 00a0 might play a role in the regulation of the state of assembly of desmin intermediate filaments.-Garbuglia, M., Verzini, M., Giambanco, I., Spreca, A., Donato, R. Effects of calcium-binding proteins (S-100a0, S-iOOa, SiOOb) on desmin assembly in vitro. FASEB J. 10, 317-324 (1996)