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

The neurofibromatosis 2 tumor suppressor gene product merlin has strong seq uence identity to the ezrin-radixin-moesin (ERM) family over its similar to 300-residue N-terminal domain, ERM proteins are membrane cytoskeletal link ers that are negatively regulated by an intramolecular association between domains known as NH2- and COOH-ERM association domains (N and C-ERMADs) tha t mask sites for binding membrane-associated proteins, such as EBP50 and E3 KARP, and F-actin. Here we show that merlin has self-association regions an alogous to the N- and C-ERMADs. Moreover, the N-/C-ERMAD interaction in mer lin is relatively weak and dynamic, and this property is reflected by the a bility of full-length recombinant merlin to form homooligomers, 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 int eraction with the ezrin N-ERMAD can be inhibited by the presence of the ezr in 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 a ffinity for the merlin N-ERMAD, The implications of these associations and the hierarchies of binding for the function and regulation of merlin and ER M proteins are discussed.