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An 88 amino-acid polypeptide from Acanthamoeba castellanii ( (Lambooy & Korn, 1986), Vandekerckhove et al, 1990).  Actobindin binds one or two actin monomers dependent on the ratios in which they are mixed.  Under conditions where actin is spontaneously polymerized by the addition of salt, actobindin causes a marked inhibition of polymerization (Lambooy & Korn, 1988), apparently by binding to an early intermediate probably dimers (Bubb et al, 1994).  The interaction of actobindin with actin is proposed to form actin dimers in a catalytic manner (Bubb et al, 1995). These actin dimers are proposed to be incapable of participation in actin polymerization (Bubb et al, 1995) and may be the so called "anti-parallel" or "upper dimers" reported by others (Millonig et al, 1988).  The structure of the antiparallel actin dimer has been solved (Bubb et al, 2002). Two identical actin binding sites in actobindin have been identified:- LKHAET (Vandekerckhove et al, 1990), which are similar to regions of other actin binding proteins, such as thymosin, Ciboulot, and Protein Kinase Cg.  Each of these motifs are covalently cross-linkable to actin (using E.D.C.) to Glu-100 and the first three amino-acids of the N-terminus of actin (Vancompernolle et al, 1991).  There is competition between actobindin and thymosin for actin-binding indicating that the similarity is not coincidence (Vancompernolle et al, 1992).

    The function of actobindin in cells appears to be to inhibit spontaneous polymerization of actin.  In support of this notion actobindin is localized (by immunofluorescence) at the base of lamellipodia and filopodia (Bubb et al, 1998).


Michael Bubb's lab in Florida USA



Bubb, M. R., Knutson, J.R., Porter, D.K. and Korn, E.D. (1994). Actobindin induces the accumulation of actin dimers that neither nucleate polymerization nor self-associate. J. Biol. Chem. 269(41): 25592-25597.

Bubb, M. R. & Korn, E. D. (1995) Kinetic model for the inhibition of actin polymerization by actobindin, Biochemistry. 34, 3921-3926.

Bubb, M. R.,Baines , I.C., and Korn, E.D. (1998). Localization of actobindin, profilin I, profilin II, and phosphatidylinositol-4,5-bisphosphate (PIP2) in Acanthamoeba castellanii. Cell Mot.Cytoskeleton 39: 134-146.

Holliday, L. S., Bubb, M. R. & Korn, E. D. (1993) Rabbit skeletal muscle actin behaves differently than Acanthamoeba actin when added to soluble extracts of Acanthamoeba castellanii., BBRC. 196, 569-575.

Millonig, R., Salvo, H. & Aebi, U. (1988) Probing actin polymerization by intermolecular cross-linking, J. Cell Biol. 106, 785-796.

Lambooy, P. K. & Korn, E. D. (1986) Purification and characterization of actobindin, a new actin monomer-binding protein from Acanthamoeba castellanii., J.Biol.Chem. 261, 17150-17155.

Lambooy, P. K. & Korn, E. D. (1988) Inhibition of an early stage of actin polymerization by actobindin., J.Biol.Chem. 263, 12836-12843.

Vancompernolle, K., Vandekerckhove, J., Bubb, M. R. & Korn, E. D. (1991) The interfaces of actin and Acanthamoeba actobindin., J.Biol.Chem. 266, 15427-15431.

Vancompernolle, K., Goethals, M., Huet, C., Louvard, D. & Vandekerckhove, J. (1992) G- to F-actin modulation by a single amino acid substitution in the actin binding site of actobindin and thymosin b4, EMBO Journal. 11, 4739-4746.

Vandekerckhove, J., Van Damme, J., Vancompernolle, K., Bubb, M. R., Lambooy, P. K. & Korn, E. D. (1990) The covalent structure of Acanthamoeba actobindin., J.Biol.Chem. 265, 12801-12805.

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