The 2.7 Å Crystal Structure of the Activated FERM Domain of Moesin: An Analysis of Structural Changes on Activation^,

Abstract

Moesin binds to a large range of proteins through its N terminal FERM (band 4.1, ezrin, radixin, moesin) domain. In full-length moesin isolated from cells, this binding is masked by binding to the C-terminal domain of moesin (C-ERMAD). Activation takes place by phosphorylation of Thr 558 in the C-ERMAD, which releases the C-ERMAD. A recently determined crystal structure of a noncovalent complex of the FERM and C-ERMAD domains showed for the first time that the structure of the FERM domain consists of three subdomains, each of which is similar to known structures. The structure reported here also contains a unique 47-residue helix pointing away from the FERM domain at the start of the alpha domain, in agreement with secondary structure predictions. Removal of the C-ERMAD does not result in a huge rearrangement of the FERM domain, but comparison with the activated radixin structure shows a consistent set of small changes. Not surprisingly, the exposed C-ERMAD binding area interacts in crystal contacts. More interestingly, a negatively charged peptide binds to the inositol site in a crystal contact and causes a greater conformational change in the structure than inositol.

Structure of the Active N-terminal Domain of Ezrin

“…The FERM domain is a clover-shaped molecule (Fig. 1A) consisting of three distinct lobes and is globally similar to structures reported previously for ERM proteins (26,31,32), merlin (38,39), and the band-4.1 protein (40). This basic structure has already been well described and will not be elaborated here.…”

“…The structures of unmasked radixin with or without IP 3 (2.8 Å resolution) were highly similar to each other, and comparison to dormant moesin showed local changes in three regions, 138 -150, 160 -178, and 243-280. The structure of activated moesin (2.7 Å resolution) also revealed shifts in these three regions (32). However, the moesin analysis was complicated by crystal packing interactions that caused large shifts in lobes F1 and -3 and concluded that consistent shifts due to activation were limited to residues 166 -170 and 260 -264.…”

“…Subsequently, structures reported for the active FERM domains of radixin with and without bound inositol (1, 4, 5)-triphosphate (IP 3 ) (31) and of moesin (32) have given some insight into the structural aspects of activation. The structures of unmasked radixin with or without IP 3 (2.8 Å resolution) were highly similar to each other, and comparison to dormant moesin showed local changes in three regions, 138 -150, 160 -178, and 243-280.…”

Structural Basis for Neurofibromatosis Type 2

“…This filamentous structure is highly consistent with 160 residues of the helical domain. Moreover, a 47-residue extended helix linked to the C-terminal of the FERM domain has been observed in the recent crystal structure of moesin (residues 1-346), which contains the FERM domain and part of the helical domain (25). As reported in this moesin structure, the extended ␣-helical segment of merlin seems to be stabilized by the hydrogen bond formation of Arg-57 from subdomain A with Glu-317 and Gln-324.…”

Model membranes to shed light on the biochemical and physical properties of ezrin/radixin/moesin

“…Conformational changes may also take place in the FERM domain, which is directly affected by membrane binding. However, comparison of crystallographic data on the FERM domain in the absence [83] or presence of the C-terminal domain [84] or of IP 3 [15] showed essentially the same organization of the 3 subdomains, with important displacements observed locally, but with no obvious loss of secondary structure elements [83,84]. Thus, in light of the available crystallographic data, modifications in the secondary structure content arise from alterations in the C-terminal domain.…”