Emerin self‐assembly mechanism: role of the LEM domain

Abstract

At the nuclear envelope, the inner nuclear membrane protein emerin contributes to the interface between the nucleoskeleton and the chromatin. Emerin is an essential actor of the nuclear response to a mechanical signal. Genetic defects in emerin cause Emery-Dreifuss muscular dystrophy. It was proposed that emerin oligomerization regulates nucleoskeleton binding, and impaired oligomerization contributes to the loss of function of emerin disease-causing mutants. We here report the first structural characterization of emerin oligomers. We identified an N-terminal emerin region from amino acid 1 to amino acid 132 that is necessary and sufficient for formation of long curvilinear filaments. In emerin monomer, this region contains a globular LEM domain and a fragment that is intrinsically disordered. Solid-state nuclear magnetic resonance analysis identifies the LEM β-fragment as part of the oligomeric structural core. However, the LEM domain alone does not self-assemble into filaments. Additional residues forming a β-structure are observed within the filaments that could correspond to the unstructured region in emerin monomer. We show that the delK37 mutation causing muscular dystrophy triggers LEM domain unfolding and increases emerin self-assembly rate. Similarly, inserting a disulfide bridge that stabilizes the LEM folded state impairs emerin N-terminal region self-assembly, whereas reducing this disulfide bridge triggers self-assembly. We conclude that the LEM domain, responsible for binding to the chromatin protein BAF, undergoes a conformational change during self-assembly of emerin N-terminal region. The consequences of these structural rearrangement and self-assembly events on emerin binding properties are discussed.

Structural analysis of the ternary complex between lamin A/C, BAF and emerin identifies an interface disrupted in autosomal recessive progeroid diseases

“…We tested binding between the tail region common to lamins A and C (LamIgF comprising aa 411 to aa 566) and these emerin fragments. As previously published, the whole emerin nucleoplasmic region from aa 1 to aa 221 is poorly soluble ( 34 ). We thus produced two overlapping emerin peptides, which we called EmN ( 26 ) and EmC (Figure 1A ).…”

“…We thus produced two overlapping emerin peptides, which we called EmN ( 26 ) and EmC (Figure 1A ). EmN (aa 1 to aa 187) comprises a LEM domain and a region that is intrinsically disordered ( 34 , 35 ). We previously showed that, in vitro , it can be observed either as a monomer or as an oligomer ( 26 ) (Figure 1B , left panel).…”

“…We suggest that lamin A/C directly interacts with emerin that is self-assembled at the nuclear envelope ( 18 , 64 ) (Figure 8 , right panel). During in vitro self-assembly, emerin exhibits a large LEM domain conformational change, strongly suggesting that self-assembled emerin does not bind BAF ( 34 ). However, we still detect proximities between lamin A/C and BAF at the nuclear periphery of interphase cells ( Supplementary Figure S5 ).…”

Rare BANF1 Alleles and Relatively Frequent EMD Alleles Including ‘Healthy Lipid’ Emerin p.D149H in the ExAC Cohort

“…However, the mechanisms by which emerin, an intrinsically disordered ‘transformer’ protein (Samson et al, 2016), senses force and signals in response to force are open questions. Emerin has at least two modes of self-association with the potential to form networks or filaments (Berk et al, 2014; Herrada et al, 2015; Samson et al, 2017). Other partners include nucleo/cytoskeletal proteins (e.g., F-actin, myosin 1c, tubulin), nuclear membrane proteins (e.g., LAP1, Samp1) and transcriptional regulators such as HDAC3, b-catenin and Lmo7 (Holaska et al, 2006; Berk et al, 2013b; Shin et al, 2013; Barton et al, 2015; Vijayaraghavan et al, 2018).…”

The Pathogenesis and Therapies of Striated Muscle Laminopathies

“…It also interacts with lamin A/C, nesprin-1α and LUMA (Ellis, 2006 ; Liang et al, 2011 ). Emerin is able to self-assemble in vitro and it was suggested that the LEM domain configuration in the emerin multimers may modulate its interaction with chromatin and nucleoplasmic proteins (Berk et al, 2014 ; Samson et al, 2017 ). Depending on tissue, emerin was also described at alternative subcellular locations.…”