Models of the actin-bound forms of the β-thymosins

In recent years two structures have been reported that demonstrate how the two halves of a β-thymosin repeat bind to actin monomers. Here we assess the validity of these structures and construct minimally biased models of the β-thymosin:actin complexes. The models reveal that the β-thymosins interact with actin throughout their length and that all the conserved residues are functional in this interface. These models are judged to be in excellent agreement with published biochemical and functional data. In particular, the models are consistent with the actin monomer sequestering and actin filament binding properties of β-thymosins. The models also correctly predict competition between thymosin-β4 with DNase I or profilin in binding actin while allowing ternary complexes at higher concentrations.