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Although
the existence of this 5kd peptide has been known for some time only
comparatively recently has
it been found to be an actin monomer sequestering agent (reviewed Huff
et al, 2001). In the platelet it is
thought to account for most of the monomeric actin pool as it is present in
these cells at a concentration of 560-600mM and binds monomeric actin with a Kd
between 0.4 and 0.7µM (Weber et al.
1992), whereas
profilin is present at 50mm
(Goldschmidt-Cleremont
et al, 1992).
Despite the fact that this protein is so small, it apparently wraps around the
actin monomer making contact with subdomains 1, 2, and 3! This is due to
the fact that the protein is extended linear molecule (Safer
et al, 1997).
Thymosin bind ATP-actin in preference to ADP-actin (Carlier
et al, 1993),
like profilin (Pantaloni
& Carlier, 1993)
but unlike ADF/cofilin (Maciver
& Weeds, 1994).
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References:-
Carlier,
M.-F., Jean, C., Rieger, K. J., Lenfant, M. & Pantaloni, D. (1993)
Modulation of the interaction between G-actin and thymosin b4
by the ATP/ADP ratio: Possible implication in the regulation of actin dynamics, Proc.
Natl. Acad. Sci. 90, 5034-5038.
Goldschmidt-Clermont,
P. J., Furman, M. I., Wachsstock, D., Safer, D., Nachmias, V. T. & Pollard,
T. D. (1992) The control of actin nucleotide exchange by Thymosin b4
and Profilin. A potential regulatory mechanism for actin polymerization in
cells, Mol.Biol.Cell. 3, 1015-1024.
Hertzog,
M., Yarnola, E. G., Didry, D., Bubb, M. R. & Carlier, M. F. (2002) Control
of actin dynamics by proteins made of b-thymosin
repeats. The actobindin family. J.Biol.Chem. 277, 14786-14792.
Huff,
T., Muller, C. S. G., Otto, A. M., Netzker, R. & Hannappel, E. (2001) b-thymosins,
small acidic peptides with multiple functions, Int. J. Biochem.Cell Biol. 33,
205-220.
Pantaloni,
D. & Carlier, M.-F. (1993) How profilin promotes actin filament assembly in
the presence of thymosin b4,
Cell. 75, 1007-1014.
Safer,
D., Sosnick, T. R. & Elzinga, M. (1997) Thymosin b4
binds actin in an extended conformation and contacts both the barbed and pointed
ends., Biochemistry. 36, 5806-5816.
Weber et al.
1992, Biochemistry, 31 6179
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