Evidence for functional homology in the F-actin binding domains of gelsolin and alpha-actinin: implications for the reqdirements of severing and capping


Abstract. The F-actin binding domains of gelsolin and c~-actinin compete for the same site on actin filaments with similar binding affinities. Both contain tandem repeats of,o125 amino acids, the first of which is shown to contain the actin-binding site. We have replaced the F-actin binding domain in the NH2-terminal half of gelsolin by that of ot-actinin. The hybrid severs filaments almost as efficiently as does gelsolin or its NH~-terminal half, but unlike the latter, requires calcium ions. The hybrid binds two actin monomers and caps the barbed ends of filaments in the presence or absence of calcium. The cap produced by the hybrid binds with lower affinity than that of gelsolin and is not stable: It dissociates from filament ends with a half life of "o15 rain. Although there is no extende

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