Opening of tandem calponin homology domains regulates their affinity for F-actin

Many actin-binding proteins contain calponin homology (CH) domains, but the manner in which these domains interact with F-actin has been controversial. Crystal structures have shown the tandem CH domains of α-actinin to be in a compact, closed conformation, but the interpretations of complexes of such tandem CH domains with F-actin have been ambiguous. We show that the tandem CH domains of α-actinin bind to F-actin in an open conformation, explaining mutations that cause human diseases, and suggesting that the opening of these domains may be one of the main regulatory mechanisms for proteins with tandem CH domains.