The β-thymosins are a family of related peptides. Recently, thymosin β4 was identified as a significant actin monomer sequestering protein in cells. To determine if other β-thymosins also bind actin, and how they may participate in the regulation of actin polymerization, we expressed thymosin β4 and its major homolog, thymosin β10, in bacteria and characterized their interactions with actin. Equilibrium sedimentation studies showed that thymosin β4 behaved as a monomeric protein in solution. Both β-thymosins bound skeletal muscle actin and inhibited actin polymerization with similar K(d) values (between 0.7-1 μM). They were not inhibited by polyphosphoinositides. Kinetic measurements showed that at high ratios of β- thymosin to actin, β-thymosin decreased the rate of barbed end filament growth. However, in spite of a close agreement between the kinetic and steady state K(d) values, the rate of barbed end filament growth was slightly, but reproducibly, larger than expected, and this deviation was particularly noticeable at lower ratios of β-thymosin to actin. We conclude that unlike profilin, β-thymosins are primarily actin monomer sequestering proteins, although some aspects of their interactions with actin are still not completely understood.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - 1993|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology