Merlin differentially associates with the microtubule and actin cytoskeleton

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Neurofibromatosis 2 (NF2) is a genetic disorder linked to the NF2 tumor suppressor gene.
• The NF2 gene encodes merlin (schwannomin), a protein similar to the ERM family (ezrin, radixin, moesin) that links the cytoskeleton to the cell membrane.
• Unlike ERM proteins, merlin lacks a conventional C-terminal actin-binding site but localizes to membrane ruffles.

Purpose of the Study:

• To investigate merlin's interaction with the actin cytoskeleton through a nonconventional binding domain.
• To determine if merlin can bind microtubules and explore the role of its conformation in this interaction.

Main Methods:

• In vitro assays to test merlin's binding to polymerized actin and microtubules.
• Analysis of merlin's N-terminal domain (residues 178-367) for actin-binding capability.
• Investigation of merlin's interaction with microtubules in different conformational states ('open' vs. 'closed').

Main Results:

• Merlin directly binds polymerized actin in vitro via an N-terminal domain (residues 178-367).
• This actin binding is unaffected by NF2 mutations or alternative splicing.
• Merlin binds polymerized microtubules in vitro through a novel N-terminal region, but only when in the 'open' conformation; the 'closed' conformation prevents microtubule binding.

Conclusions:

• Merlin directly interacts with the actin cytoskeleton through a nonconventional N-terminal actin-binding domain.
• Merlin's interaction with microtubules is conformation-dependent, suggesting a regulatory mechanism for its function.
• These findings support the model of merlin existing in 'open' and 'closed' conformations relevant to its role as a negative growth regulator.