Dimerization of elongator protein 1 is essential for Elongator complex assembly

Abstract

The evolutionarily conserved Elongator complex, which is composed of six subunits elongator protein 1 (Elp1 to -6), plays vital roles in gene regulation. The molecular hallmark of familial dysautonomia (FD) is the splicing mutation of Elp1 [also known as IκB kinase complex-associated protein (IKAP)] in the nervous system that is believed to be the primary cause of the devastating symptoms of this disease. Here, we demonstrate that disease-related mutations in Elp1 affect Elongator assembly, and we have determined the structure of the C-terminal portion of human Elp1 (Elp1-CT), which is sufficient for full-length Elp1 dimerization, as well as the structure of the cognate dimerization domain of yeast Elp1 (yElp1-DD). Our study reveals that the formation of the Elp1 dimer contributes to its stability in vitro and in vivo and is required for the assembly of both the human and yeast Elongator complexes. Functional studies suggest that Elp1 dimerization is essential for yeast viability. Collectively, our results identify the evolutionarily conserved dimerization domain of Elp1 and suggest that the pathological mechanisms underlying the onset and progression of Elp1 mutation-related disease may result from impaired Elongator activities.F amilial dysautonomia (FD) (Online Mendelian Inheritance in Man: 223900), which is an Ashkenazi Jewish disorder with an incidence of 1:3,700 live births, is an autosomal recessive disorder that affects the development and survival of sensory, sympathetic, and some parasympathetic neurons (1). FD patients are characterized by cardiovascular instability, gastrointestinal dysfunction, vomiting crises, decreased sensitivity to pain and temperature, and recurrent pneumonias (2). The most common mutation, which represents >99.5% of all FD patients, is a T-to-C transition in position six of the donor splice site of intron 20 in the gene transcript of the IκB kinase (IKK) complex-associated protein (IKAP), also known as elongator protein 1 (Elp1) (3, 4). This splicing mutation causes skipping of exon 20 and results in encoding a truncated IKAP/Elp1 protein (referred to as Elp1-FD hereafter) (Fig. 1A).IKAP/Elp1 was originally identified as a scaffold protein and a regulator for IKKs involved in proinflammatory cytokine signaling (5). However, contrary to this observation, subsequent analyses failed to demonstrate an association with IKKs (6). Coincident and subsequent studies supported the notion that IKAP/Elp1 is a component of the highly conserved Elongator complex from different species (7-9) (for simplicity, the term Elp1 will be used in the following discussion). The holo-Elongator complex contains six subunits (Elp1 to -6) and assembles into a core subcomplex (Elp1 to -3) and an accessory subcomplex (Elp4 to -6), which is involved in substrate recognition (10, 11). Moreover, the holo-Elongator is a functional unit, as illustrated in yeast, in which strains lacking any of the six Elp proteins exhibit similar phenotypes (7,12,13), and in that the removal of any Elongator subunits affects the...

Architecture of the yeast Elongator complex

“…Thus, although most of the Elongator density has the shape of a nearly symmetrical two‐lobed structure, the Elp456 ring binds to the complex asymmetrically. The C‐terminal domain (CTD) of Elp1 observed in the crystal structure 29 can be also unambiguously fitted to the holoElongator model (Fig 1F). The Elp1‐CTD fits to the arch of the Elongator complex with higher scores than in other locations.…”

Phosphatidylserine Ameliorates Neurodegenerative Symptoms and Enhances Axonal Transport in a Mouse Model of Familial Dysautonomia

“…IKAP was previously suggested to impact histone acetylation as part of the Elongator complex [26–29], and levels of mRNA encoding the catalytic histone acetyltransferase subunit of Elongator protein 3 (ELP3) were significantly downregulated in CKO Tyrp2 FD mice compared to control littermates (Fig 1L). We therefore examined the effect of IKAP depletion on acetylation of histone H3K9.…”

“…Early findings indicated that IKAP (also known as ELP1) is a subunit of the Elongator complex, important for RNA polymerase II transcription elongation in the nucleus and for histone acetylation [25–29]. As IKAP co-localizes and purifies with cytoplasmic proteins [30–32], it has been suggested that IKAP functions in tRNA modification [33–35], exocytosis [36], cell adhesion and migration, microtubule organization [20,32,37,38], p53 activation [39], and c-Jun N-terminal kinase (JNK) signaling pathway regulation [19,23,31].…”

Familial Dysautonomia: Mechanisms and Models

“…Although the predicted truncated IKAP protein of 79 kDa has been detected in FD-derived lymphoblasts (Anderson et al , 2001), other groups failed to detect such product in other FD cell lines or tissues. It is currently believed that at least part of the abnormally spliced IKBKAP transcripts is degraded by nonsense-mediated mRNA decay (NMD), as demonstrated in FD-derived olfactory stem cells (Boone et al , 2010) and that the truncated protein might be unstable due to its inability to dimerize (Xu et al , 2015). …”