Structural and biochemical insights into Zn-bound EF-hand proteins, EFhd1 and EFhd2.

EF-hand proteins, which contain a Ca-binding EF-hand motif, are involved in regulating diverse cellular functions. Ca 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, including Mg, Pb and Zn, 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-independent actin-binding and Ca-dependent actin-bundling activity. Although Ca 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 ions within their EF-hands are reported. The presence of Zn 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-independent actin-binding and Zn-dependent actin-bundling activity. This suggests the actin-related activities of EFhd1 and EFhd2 could be regulated by Zn as well as Ca.