Structural implications of Ca2+-dependent actin-bundling function of human EFhd2/Swiprosin-1

Sci Rep. 2016 Dec 15:6:39095. doi: 10.1038/srep39095.

Abstract

EFhd2/Swiprosin-1 is a cytoskeletal Ca2+-binding protein implicated in Ca2+-dependent cell spreading and migration in epithelial cells. EFhd2 domain architecture includes an N-terminal disordered region, a PxxP motif, two EF-hands, a ligand mimic helix and a C-terminal coiled-coil domain. We reported previously that EFhd2 displays F-actin bundling activity in the presence of Ca2+ and this activity depends on the coiled-coil domain and direct interaction of the EFhd2 core region. However, the molecular mechanism for the regulation of F-actin binding and bundling by EFhd2 is unknown. Here, the Ca2+-bound crystal structure of the EFhd2 core region is presented and structures of mutants defective for Ca2+-binding are also described. These structures and biochemical analyses reveal that the F-actin bundling activity of EFhd2 depends on the structural rigidity of F-actin binding sites conferred by binding of the EF-hands to Ca2+. In the absence of Ca2+, the EFhd2 core region exhibits local conformational flexibility around the EF-hand domain and C-terminal linker, which retains F-actin binding activity but loses the ability to bundle F-actin. In addition, we establish that dimerisation of EFhd2 via the C-terminal coiled-coil domain, which is necessary for F-actin bundling, occurs through the parallel coiled-coil interaction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism*
  • Calcium / metabolism*
  • Calcium-Binding Proteins / chemistry*
  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / metabolism*
  • Crystallography, X-Ray
  • Humans
  • Models, Molecular
  • Mutation
  • Protein Binding
  • Protein Domains
  • Protein Structure, Tertiary

Substances

  • Actins
  • Calcium-Binding Proteins
  • EFHD2 protein, human
  • Calcium