An actin-depolymerizing protein (depactin) from starfish oocytes: properties and interaction with actin.

Abstract

Physico-chemical properties and interaction with actin of an actin-depolymerizing protein from mature starfish oocytes were studied. This protein, which is called depactin, exists in a monomeric form under physiological conditions. Its molecular weight is "--20,000 for the native protein and ~,17,000 for denatured protein. The Glu + Asp/Lys + Arg molar ratio of this protein is 1.55. The apparent pl of the denatured depactin is ~6.The extent of actin polymerization is reduced by the presence of depactin; however, the rate of polymerization seems to be accelerated as measured spectrophotometrically at 238om. This effect is interpreted to indicate that depactin cut the newly formed filaments into small fragments, thereby increasing the number of the filament ends to which monomers are added. The apparent critical concentration of actin for polymerization, as determined by viscometry or flow birefringence measurement, is increased by the presence of depactin in a concentration-dependent manner. Raising the pH of the solution does not reverse the action of depactin. The molar ratio of actin and depactin, which interact with each other, is estimated to be 1:1 by means of a cross-linking experiment using a water-soluble carbodiimide. Depactin binds to a DNase I-Sepharose column via actin and is selectively eluted with 0.6 M KCI or 0.6 M KI. The association constant between actin and depactin is estimated, using the column, to be 2-3 x 106M -1.The content of depactin in the high-speed supernatant of the oocyte extract is determined to be 1%; this can act upon '--63% of the actin in the supernatant.

The actin filament severing protein actophorin promotes the formation of rigid bundles of actin filaments crosslinked with alpha-actinin.

“…In the fibroblast, a progression of cytoskeletal arrangements is seen from the newly polymerized actin network at the leading edge (Wang, 1985), to the production of "arcs" (Heath, 1983) composed of small bundles of filaments which are continually swept towards the nucleus where an arrangement oflarger perinuclear actin bundles known as the cellular geodome is found . As actophorin-like proteins (Mabuchi, 1983;Bamburg et al, 1980) and gelsolin (another actin filament severing protein), have been isolated from a number of vertebrate sources, it is possible that severing activity in concert with crosslinking proteins also found in protruding lamella (Geiger et al, 1984) form an increasingly anisotropic gel by a mechanism similar to that postulated here.…”

Ultrastructural studies of the morphological variations of the egg surface and envelopes of the African catfish <em>Clarias gariepinus</em> (Burchell, 1822) before and after fertilisation with a discussion of fertilisation mechanism

“…echinoderms (Vacquier, 1981), the cortical layer of the egg was considered to be a gel with specialised viscoelastic mechanical properties (Hart, 1990). Moreover, the egg cortex became increasingly contractile after sperm-egg union, causing a twisting movement of oil droplets toward the animal pole; a meshwork of polymerised actin appeared in the egg cytoplasm and microfilaments became highly organised in the microvilli (Vacquier, 1981;Mabuchi, 1983). Griffin et al (1996) Gasterosteus aculeatus 19.4, 36.7, 39.4, 42.9, 46.1, 53 kDa Deung et al (1999 Celius and Walther (1998) Actin and actin-containing filaments have been described in the cortical layer of Brachydanio (Wolenski and Hart, 1988) and Oncorhynchus (Kobayashi, 1985) eggs.…”

Hyperosmotic stress‐induced reorganization of actin bundles in Dictyostelium cells over‐expressing cofilin

“…The cofilin family consists of cofilin, a low molecular weight actin-regulating protein (Nishida et al 1984a;Yahara et al 1996), and its related proteins including destrin/actin-depolymerizing factor (Bamburg et al 1980;Nishida et al 1985), actophorin , and depactin (Mabuchi 1983). Members of the cofilin family distribute ubiquitously among eukaryotes and are essential for viability in S. cerevisiae (Iida et al 1993;Moon et al 1993), Caenorhabditis elegans (Mckim et al 1994), Drosophila melanogaster (Gunsalus et al 1995), D. discoideum (Aizawa et al 1995), and Xenopus laevis (Abe et al 1996).…”