Structural and biochemical insights into Zn(2+)-bound EF-hand proteins, EFhd1 and EFhd2

EF-hand proteins, which contain a Ca(2+)-binding EF-hand motif, are involved in regulating diverse cellular functions. Ca(2+) binding induces conformational changes that modulate the activities of EF-hand proteins. Moreover, these proteins occasionally modify their activities by coordinating metals other than Ca(2+), including Mg(2+), Pb(2+) and Zn(2+), within their EF-hands. EFhd1 and EFhd2 are homologous EF-hand proteins with similar structures. Although separately localized within cells, both are actin-binding proteins that modulate F-actin rearrangement through Ca(2+)-independent actin-binding and Ca(2+)-dependent actin-bundling activity. Although Ca(2+) is known to affect the activities of EFhd1 and EFhd2, it is not known whether their actin-related activities are affected by other metals. Here, the crystal structures of the EFhd1 and EFhd2 core domains coordinating Zn(2+) ions within their EF-hands are reported. The presence of Zn(2+) within EFhd1 and EFhd2 was confirmed by analyzing anomalous signals and the difference between anomalous signals using data collected at the peak positions as well as low-energy remote positions at the Zn K-edge. EFhd1 and EFhd2 were also found to exhibit Zn(2+)-independent actin-binding and Zn(2+)-dependent actin-bundling activity. This suggests the actin-related activities of EFhd1 and EFhd2 could be regulated by Zn(2+) as well as Ca(2+).