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Thymosin b4  

Updated 21/5/02

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 0.7ÁM (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).


  Hannappel Lab



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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