Hierarchy of Merlin and Ezrin N- and C-terminal Domain Interactions in Homo- and Heterotypic Associations and their Relationship to Binding of Scaffolding Proteins EBP50 and E3KARP

Abstract

The neurofibromatosis 2 tumor suppressor gene product merlin has strong sequence identity to the ezrin-radixin-moesin (ERM) family over its ∼300-residue N-terminal domain. ERM proteins are membrane cytoskeletal linkers that are negatively regulated by an intramolecular association between domains known as NH2- and COOH-ERM association domains (N- and C-ERMADs) that mask sites for binding membrane-associated proteins, such as EBP50 and E3KARP, and F-actin. Here we show that merlin has self-association regions analogous to the N- and C-ERMADs. Moreover, the N-/C-ERMAD interaction in merlin is relatively weak and dynamic, and this property is reflected by the ability of full-length recombinant merlin to form homo-oligomers. Remarkably, the merlin C-ERMAD has a higher affinity for the N-ERMAD of ezrin than the N-ERMAD of merlin. Both the ezrin and merlin N-ERMAD bind EBP50. This interaction with the ezrin N-ERMAD can be inhibited by the presence of the ezrin C-ERMAD, whereas interaction with the merlin N-ERMAD is not inhibited by either C-ERMAD. E3KARP binds tightly to the ezrin N-ERMAD but has little affinity for the merlin N-ERMAD. The implications of these associations and the hierarchies of binding for the function and regulation of merlin and ERM proteins are discussed.