• radixin;
  • ERM;
  • FERM domain;
  • masking.

ERM (ezrin/radixin/moesin) proteins bind to the cytoplasmic tail of adhesion molecules in the formation of the membrane-associated cytoskeleton. The binding site is located in the FERM (4.1 and ERM) domain, a domain that is masked in the inactive form. A conventional masking motif, strand 1 (residues 494–500 in radixin), has previously been identified in the C-terminal tail domain. Here, the crystal structure of dimerized radixin FERM domains (residues 1–310) is presented in which the binding site of one molecule is occupied by the C-­terminal residues (residues 295–304, strand 2) of the other molecule. The residues contain a conserved motif that is compatible with that identified in the adhesion molecules. The residues might serve as a second masking region in the inactive form of ERM proteins.