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
& 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
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
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).
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):
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.
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.
R., Salvo, H. & Aebi, U. (1988) Probing actin polymerization by
intermolecular cross-linking, J. Cell Biol. 106, 785-796.
P. K. & Korn, E. D. (1986) Purification and characterization of actobindin,
a new actin monomer-binding protein from Acanthamoeba castellanii., J.Biol.Chem.
P. K. & Korn, E. D. (1988) Inhibition of an early stage of actin
polymerization by actobindin., J.Biol.Chem. 263, 12836-12843.
K., Vandekerckhove, J., Bubb, M. R. & Korn, E. D. (1991) The interfaces of
actin and Acanthamoeba actobindin., J.Biol.Chem. 266, 15427-15431.
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.
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.