A 45,000-mol-wt protein-actin complex from unfertilized sea urchin egg affects assembly properties of actin.

Abstract

A one-to-one complex of a 45,000-mol-wt protein and actin was purified from unfertilized eggs of the sea urchin, Hemicentrotus pulcherrimus, by means of DNase ISepharose affinity and gel filtration column chromatographies. Effects of the complex on the polymerization of actin were studied by viscometry, spectrophotometry, and electron microscopy. The results are summarized as follows: (a) The initial rate of actin polymerization is inhibited at a very low molar ratio of the complex to actin. (b) Acceleration of the initial rate of polymerization occurs at a relatively high, but still substoichiometric, molar ratio of the complex to actin. (c) Annealing of F-actin fragments is inhibited by the complex. (d) The complex prevents actin filaments from depolymerizing. (e) Growth of the actin filament is inhibited at the barbed end. In all cases except b, a molar ratio of less than 1:100 of the 45,000-mol-wt protein-actin complex to actin is sufficient to produce these significant effects. These results indicate that the 45,000-mol-wt protein-actin complex from the sea urchin egg regulates the assembly of actin by binding to the barbed end (preferred end or rapidly growing end) of the actin filament. The 45,000-mol-wt protein-actin complex can thus be categorized as a capping protein.

Relative changes in F-actin during the first cell cycle: Evidence for two distinct pools of F-actin in the sea urchin egg

“…The accumulation of F-actin into microvilli after fertilization may be caused by the rise in intracellular Ca2' at fertilization [Begg et al, 19821. It is noteworthy that the shift in actin from the TSF pool to the TIF pool in PMN leukocytes is regulated by an increase in Ca2+ and is thought to be mediated by gelsolin [Watts et al, 19951. Ca2+-sensitive proteins of 45 K and 100 K exist in the sea urchin egg that may function similarly to gelsolin in the PMN leukocyte [Hosoya and Mabuchi, 1984;Wang and Spudich, 1984;Hosoya et al, 19861. Analysis of the distribution of these proteins in the soluble and insoluble pools of the sea urchin egg before and after fertilization would determine if these proteins function in formation of the insoluble F-actin cytoskeleton.…”

Probing nucleation, cutting and capping of actin filaments

“…A lack of filament formation at an end indicates binding of a capping protein. Electron microscopy has turned out to be a superior method for determination of the end to which a capping protein binds, as the morphology of actin filaments decorated by heavy meromyosin or of microvillus cores permits distinction between the barbed and pointed ends (Maruyama et al, 1977;Isenberg et al, 1980;Harris & Weeds, 1984;Hosoya & Mabuchi, 1984;Oosawa et al, 1987).…”

A novel protein accumulated during maturation of the pods of the plantImpatiens balsamina

“…But this protein produced short actin filaments like capping or severing proteins. The short filaments are unequal in size like fragmin [38] or villin [39] induced shortening of actin filaments. This protein is apparently similar to the capping or severing group of proteins.…”