The Actin Filament: Severing Domain of Plasma Gelsolin

• Published in: The Journal of cell biology Vol. 103; no. 4; pp. 1473 - 1481
• Main Authors: Chaponnier, Christine, Janmey, Paul A., Yin, Helen L.
• Format: Journal Article
• Language: English
• Published: New York, NY Rockefeller University Press 01.10.1986; The Rockefeller University Press
• Subjects: Actin Cytoskeleton - metabolism; Actins; Actins - metabolism; Amino Acid Sequence; Amino acids; Antibodies; Antibodies, Monoclonal - immunology; Binding Sites; Biochemistry; Biological and medical sciences; Blood plasma; Calcium - pharmacology; Calcium-Binding Proteins - immunology; Calcium-Binding Proteins - metabolism; Cell structures and functions; Cytoskeleton - metabolism; Cytoskeleton, cytoplasm. Intracellular movements; Fundamental and applied biological sciences. Psychology; Gels; Gelsolin; Humans; Microfilament Proteins - immunology; Microfilament Proteins - metabolism; Microfilaments; Molecular and cellular biology; Molecules; Monomers; Polymerization; Protein Binding; Thermolysin; Human; Binding protein; Calcium; Actins; Contractile protein; Molecular interaction; Binding site; Blood; Blood plasma
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.103.4.1473

Gelsolin, a multifunctional actin-modulating protein, has two actin-binding sites which may interact cooperatively. Native gelsolin requires micromolar Ca2+ for optimal binding of actin to both sites, and for expression of its actin filament-severing function. Recent work has shown that an NH2-terminal chymotryptic 17-kD fragment of human plasma gelsolin contains one of the actin-binding sites, and that this fragment binds to and severs actin filaments weakly irrespective of whether Ca2+ is present. The other binding site is Ca2+ sensitive, and is found in a chymotryptic peptide derived from the COOH-terminal two-thirds of plasma gelsolin; this fragment does not sever F-actin or accelerate the polymerization of actin. This paper documents that larger thermolysin-derived fragments encompassing the NH2-terminal half of gelsolin sever actin filaments as effectively as native plasma gelsolin, although in a Ca2+-insensitive manner. This result indicates that the NH2-terminal half of gelsolin is the actin-severing domain. The stringent Ca2+ requirement for actin severing found in intact gelsolin is not due to a direct effect of Ca2+ on the severing domain, but indirectly through an effect on domains in the COOH-terminal half of the molecule to allow exposure of both actin-binding sites.