Control of actin assembly by the WH2 domains and their multifunctional tandem repeats in Spire and Cordon-Bleu.

The WASP-homology 2 (WH2) domain is a 5-kDa actin-binding protein module that attracts increasing interest by its multifunctional regulation of actin dynamics in motile and morphogenetic processes. Identified by a short consensus sequence LKKT/V originally found in the actin-sequestering ß-thymosin peptides, the ßT/WH2 domains are inserted in a large number of proteins, in particular, the WASP proteins involved in cell protrusions. WH2 are found in tandem repeats in proteins involved in early development and axis-patterning processes, like Spire and Cordon-Bleu. These intrinsically disordered proteins regulate actin assembly in an adaptive and versatile fashion by a fine control of local interaction dynamics within the WH2-actin complex. Versatility is amplified by the protein environment in which the WH2 domain is inserted and by synergy with other adjacent actin-binding modules. Multifunctional activities emerge in WH2 repeats, including filament nucleation, dramatic severing, and barbed end capping or tracking. WH2 domains thus are instrumental in designing customized actin regulators.