Cordon-Bleu uses WH2 domains as multifunctional dynamizers of actin filament assembly

Cordon-Bleu is, like Spire, a member of the growing family of WH2 repeat proteins, which emerge as versatile regulators of actin dynamics. They are expressed in morphogenetic and patterning processes and nucleate actin assembly in vitro. Here, we show that Cordon-Bleu works as a dynamizer of actin assembly by combining many properties of profilin with weak filament nucleating and powerful filament severing activities and sequestration of ADP-actin, which altogether generate oscillatory polymerization kinetics. A short lysine-rich sequence, N-terminally adjacent to the three WH2 domains, is required for nucleation and severing. In this context, nucleation requires only one WH2 domain, but filament severing requires two adjacent WH2 domains. A model integrating the multiple activities of Cordon-Bleu and quantitatively fitting the multiphasic polymerization curves is derived. Hence, with similar structural organization of WH2 repeats, Cordon-Bleu and Spire display different functions by selecting different sets of the multifunctional properties of WH2 domains.