Thymosin beta 10 and thymosin beta 4 are both actin monomer sequestering proteins.
The beta-thymosins are a family of related peptides. Recently, thymosin beta 4 was identified as a significant actin monomer sequestering protein in cells. To determine if other beta-thymosins also bind actin, and how they may participate in the regulation of actin polymerization, we expressed thymosin beta 4 and its major homolog, thymosin beta 10, in bacteria and characterized their interactions with actin. Equilibrium sedimentation studies showed that thymosin beta 4 behaved as a monomeric protein in solution. Both beta-thymosins bound skeletal muscle actin and inhibited actin polymerization with similar Kd values (between 0.7-1 microM). They were not inhibited by polyphosphoinositides. Kinetic measurements showed that at high ratios of beta-thymosin to actin, beta-thymosin decreased the rate of barbed end filament growth. However, in spite of a close agreement between the kinetic and steady state Kd 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 beta-thymosin to actin. We conclude that unlike profilin, beta-thymosins are primarily actin monomer sequestering proteins, although some aspects of their interactions with actin are still not completely understood.
SciCrunch is a data sharing and display platform. Anyone can create a custom portal where they can select searchable subsets of hundreds of data sources, brand their web pages and create their community. SciCrunch will push data updates automatically to all portals on a weekly basis. User communities can also add their own data to scicrunch, however this is not currently a free service.