Evidence for Functional Homology in the F-Actin Binding Domains of Gelsolin and α-Actinin: Implications for the Requirements of Severing and Capping

• Published in: The Journal of cell biology Vol. 119; no. 4; pp. 835 - 842
• Main Authors: Way, M., Pope, B., Weeds, A. G.
• Format: Journal Article
• Language: English
• Published: New York, NY Rockefeller University Press 01-11-1992; The Rockefeller University Press
• Subjects: Actinin - chemistry; Actinin - metabolism; Actins; Actins - metabolism; Amino Acid Sequence; Amino acids; Analytical, structural and metabolic biochemistry; Binding Sites; Biological and medical sciences; Calcium; Calcium-Binding Proteins - chemistry; Calcium-Binding Proteins - metabolism; Contractile proteins; Depolymerization; Fluorescence; Fundamental and applied biological sciences. Psychology; Gelsolin; Holoproteins; Microfilament Proteins - chemistry; Microfilament Proteins - metabolism; Microfilaments; Molecular Sequence Data; Monomers; Polymerization; Proteins; Viscosity; Actins; Microfilament; Binding protein; Homology; Capping; Binding site
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.119.4.835

The F-actin binding domains of gelsolin and α-actinin compete for the same site on actin filaments with similar binding affinities. Both contain tandem repeats of ∼125 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 α-actinin. The hybrid severs filaments almost as efficiently as does gelsolin or its NH2-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 ∼15 min. Although there is no extended sequence homology between these two different F-actin binding domains, our experiments show that they are functionally equivalent and provide new insights into the mechanism of microfilament severing.