J. Biochem, 1988, Vol. 104, No. 1 72-80
© 1988 Japanese Biochemical Society
research-article |
A Novel Actin Filament-Capping Protein from Sea Urchin Eggs: A 20,000-Molecular-Weight Protein-Actin Complex1
Department of Biology, College of Arts and Sciences, The University of Tokyo Komaba, Meguro-ku, Tokyo 153
1 To whom correspondence should be addressed
A novel protein factor which reduces the low-shear viscosity of rabbit skeletal muscle actin was purified from a 0.6 M KCI-extract of an insoluble fraction of sea urchin eggs by ammonium sulfate fractionation, gel filtration column chromatography, DNase I column chromatography, and hydroxylapatite column chromatography. This protein factor was shown to be a one-to-one complex of a 20,000-molecular-weight protein and egg actin. This protein complex accelerated the initial rate of actin polymerization, but reduced the steady-state viscosity of F-actin. It inhibited at substoichiometric amounts the elongation of actin filaments on sonicated F-actin fragments and depolymerization of F-actin induced by dilution. In addition, it increased the critical concentration of actin for polymerization. All these effects of this protein complex on actin could be explained by the "capping the barbed end" of the actin filament by the complex. The 20,000-molecular-weight protein which was separated from actin also possessed the barbed end-capping activities, but differed from the complex in that it did not accelerate the polymerization of actin.
1 This paper is paper VII in the series Actin-Modulating Proteins in the Sea Urchin Egg. Paper VI: Mabuchi, I. & Kane, RE. (1987) J. Biochem. 102, 947–956. This work was supported by a Grant-in-Aid from the Ministry of Education, Science and Culture of Japan and bya research grant from Toray Science Foundation.
2 Present address: Adachi Research Laboratories, Shiseido Research Center, Nippa-cho,Kohoku-ku, Yokohama, Kanagawa 223.