J. A., Blum, J. D. Williams, R.C. & Pollard, T.D. (1986)
Purification and Characterization of Actophorin, a New 15,000-Dalton
Actin-binding Protein from Acanthamoeba castellanii. J. Biol.
Chem. 261, 477-485.
Actophorin is a new actin-binding protein from Acanthamoeba
castellanii that consists of a single polypeptide with a
molecular weight of 15,000. The isoelectric point is 6.1, and
amino acid analysis shows an excess of acidic residues over
basic residues. The phosphate content is less than 0.2 mol/mol.
There is 0.4 +/- 0.1 mg of actophorin/g of cells, so that the molar
ratio of actin to actophorin is about 10:1 in the cell. Unique two-dimensional
maps of tryptic and chymotryptic peptides and complete absence
of antibody cross-reactivity show that Acanthamoeba actophorin,
profilin, capping protein, and actin are separate gene products
with minimal homology. Actophorin has features of both an
actin monomer-binding protein and an actin filament-severing
protein. Actophorin reduces the extent of actin
polymerization at steady state in a concentration-dependent fashion
and forms a complex with pyrene-labeled actin that has spectral properties
of unpolymerized actin. During ultracentrifugation a complex of actophorin
and actin sediments more rapidly than either actin monomers or actophorin.
Although actophorin inhibits elongation at both ends of actin filaments,
it accelerates the late stage of spontaneous polymerization like mechanical
shearing and theoretical predictions of polymer fragmentation. Low
concentrations of actophorin decrease the length and the low shear viscosity
of actin filaments. High concentrations cause preformed filaments to
shorten rapidly. Ca2+ is not required for any of these effects. Muscle
and amoeba actin are equally sensitive to actophorin.
Identification and purification of an ADF/cofilin member from a soil