Mutationen in Genen, die für Kernhüllproteine codieren sind mit einer stetig zunehmenden Anzahl menschlicher Erkrankungen verbunden, die als Envelopathien bezeichnet werden. Erstaunlicherweise betrifft die Pathologie dieser Krankheiten spezifische Gewebe und Organe, obwohl entsprechende Proteine meist ubiquitär exprimiert werden. So führen beispielsweise Defekte in Emerin, einem Protein der inneren Kernhülle, zur X-chromosomalen Emery- Dreifuss Muskeldystrophie (EDMD). Diese Krankheit ist durch Muskelschwäche oder – schwund gekennzeichnet. Defekte im Kernhüllprotein MAN1 sind dagegen mit Krankheiten verbunden, die Knochen- und Hautgewebe betreffen. Interessanterweise besitzen beide Proteine eine evolutionär hoch konservierte Domäne, die sog. LEM-Domäne. LEM-Domänen Proteine können mit der Kernlamina interagieren, ebenso mit dem sog. Barrier-to- Autointegration Factor (BAF) sowie mit zahlreichen Transkriptionsfaktoren. Dennoch ist die funktionelle Rolle der LEM-Domänen Proteine bis dato nicht vollständig aufgeklärt. In der vorliegenden Studie sollten daher die Funktionen von MAN1 und Emerin während der Frühentwicklung von Xenopus laevis untersucht werden. Vorangehende Untersuchungen zeigten, dass Mikroinjektionen von XMAN1- Antikörpern in Zwei-Zell-Stadien befruchteter Eizellen zu einem Arrest der Zellteilung in der injizierten Blastomere führten. Da dabei eine Störung der Kernhüllbildung spekuliert wurde, sollte durch Antikörper-vermittelter Inhibition von XMAN1 die Bildung von in vitro Kernen im Xenopus Eiextrakt untersucht werden. Dabei wurden Kerne beobachtet, die dekondensiertes Chromatin zeigten, bei denen jedoch eine Fusion von Membranvesikeln zu einer durchgehenden Kernhülle nicht stattgefunden hatte. Frühere Charakterisierungen von MAN1 und Emerin zeigten unterschiedliche Expressionsmuster während der Entwicklung von X. laevis. Da XMAN1 ubiquitär exprimiert und Xemerin jedoch erstmals ab Stadium 41 nachweisbar ist, war es mittels Mikroinjektion von Xemerin möglich zu zeigen, dass es in der Lage ist den Arrest der Zellteilung zu verhindern. Es wurde daher die These aufgestellt, dass MAN1 und Emerin während der Frühentwicklung von Xenopus überlappende Funktionen besitzen. Um diese These zu prüfen, wurde zunächst unter Verwendung des Proximity Ligation Assays untersucht, ob beide Proteine miteinander interagieren können. Mit Hilfe dieser Methode konnte gezeigt werden, dass Interaktionen beider Proteine innerhalb der Kernhülle lokalisieren. Die Interaktionen blieben während der Mitose bestehen und waren erst wieder zum Ende der Mitose in der Kernhülle nachweisbar. Diese Resultate deuten daher darauf hin, dass XMAN1/Xemerin-Interaktionen während der ... / Mutations in genes encoding for nuclear envelope proteins are linked to an increasing number of human diseases, called envelopathies. Interestingly, pathology of these diseases affects specific tissues and organs, even though the related proteins are expressed ubiquitous. Defects in the inner nuclear membrane protein emerin for example, are leading to X-linked Emery- Dreifuss muscular dystrophy (EDMD), characterized by muscle weakness or wasting. Conversely, defects in the nuclear envelope protein MAN1 are linked to bone and skin disorders. Both proteins share a highly conserved domain, called LEM-domain. LEM proteins are known to interact with the nuclear lamina, the so called Barrier-to-Autointegration Factor (BAF) and several transcription factors. Nevertheless, knowledge of the functional roles of LEM proteins is still unclear. For this reason, this study aimed to investigate the roles of MAN1 and emerin during early Xenopus laevis development and nuclear envelope assembly. ...

Mutationen im humanen Emerin-Gen verursachen beim Menschen eine angeborene Muskelschwäche, die X-gebundene Emery-Dreifuss. Der Phänotyp dieser Störung manifestiert sich in der zweiten und dritten Lebensdekade durch Verkürzungen der Nacken , Ellenbogen- und Achillessehnen, progressiven Muskelschwund am Oberkörper sowie Störung der Reizweiterleitung und eine Kardiomyopathie. Zwar wurden die Funktionen dieses ubiquitären Kernmembranproteins bislang intensiv erforscht, allerdings blieben die krankheitsverursachenden Mechanismen, die für den späten Ausbruch der gewebespezifischen Erkrankung verantwortlich sind, noch weitestgehend unverstanden. Um Erkenntnisse über die pathologische(n) Funktion(en) des integralen Membranproteins Emerin zu gewinnen, wurde dessen spatio-temporäre Transkriptions- und Expressionsmuster während der frühen Embryonalentwicklung im Modellsystem Xenopus laevis charakterisiert. Durch EST-Datenbankanalysen konnten in der pseudotetraploiden Spezies zwei Emerin-Gene (Xemerin1 und -2) identifiziert werden. Im Unterschied zu dem längeren Säuger-Emerin (254 Reste bei Homo sapiens ) konnte allerdings kein Kernlokalisationssignal und auch kein serinreicher Sequenzbereich festgestellt werden. Durch Herstellung monoklonaler Antikörper wurde die subzelluläre und gewebespezifische Lokalisation der Xemerin-Proteine untersucht. Interessanterweise war Xemerin weder in der Immunfluoreszenz noch im Immunblot in Oozyten nachweisbar. Mit dem zweidimensionalen Gelektrophorese-Verfahren NEPHGE konnte gezeigt werden, dass der von uns hergestellte monoklonale Antikörper 59/7 beide Xemerin-Formen erkannte und die Proteine durch unterschiedliche molekulare Massen und isoelektrische Punkte voneinander zu trennen waren. Durch Immunoblotting embryonaler Proteine aus unterschiedlichen Entwicklungsstadien konnte gezeigt werden, dass Xemerin1 und -2 im Laufe der Embryogenese von Xenopus laevis erstmals im Entwicklungsstadium 43 exprimiert werden. Unerwarteterweise konnte durch RT-PCR-Analysen eine Aktivität der Xemerin-Gene während der gesamten Embryogenese belegt werden. Northernblot- und Sequenzanalysen der Xemerin-mRNA zeigten außerordentlich große untranslatierte Bereiche mit snRNP-Bindungsmotiven. Durch zwei voneinander unabhängige Analyseverfahren wurde festgestellt, dass die Xemerin-Genaktivität ab dem Stadium 30 deutlich zunahm. Äußerst interessant war in diesem Zusammenhang die Beobachtung, dass exakt zu diesem Zeitpunkt die Aktivität des XMAN1-Gens, einem weiteren Protein der inneren Kernmembran, signifikant herunterreguliert wurde. Whole-mount in situ Hybridisierungsversuche zeigten einen Xemerin-Expressionsschwerpunkt in neuro-ektodermalen Geweben von Tadpole-Embryonen, wie dies auch von XMAN1 (auch SANE genannt) berichtet wurde. Aufgrund dieser Erkenntnisse wurde angenommen, dass Xemerin und XMAN1 überlappende Funktionen aufweisen. Durch die Herstellung rekombinanter Fusionproteine konnte gezeigt werden, dass XMAN1 eine identische subzelluläre Verteilung wie Xemerin aufwies. In vitro Bindungsassays wiesen eine direkte Wechselwirkung von XMAN1 mit beiden Xemerin-Formen sowie mit Xenopus Lamin A nach. Diese Arbeit konnte durch die Charakterisierung von Xenopus Emerin die Grundlagen für weitere intensive Forschungen legen und zeigt eindeutig, dass das Modellsystem Xenopus laevis mit dem Säugermodell Maus konkurrenzfähig ist, um die krankheitsverursachende Mechanismen der Emery-Dreifuss Muskeldystrophie aufzuklären. / Mutations in the human emerin gene EMD cause a rare form of an inheritated muscle dysfunction of striated muscle, named Emery-Dreifuss muscular dystrophy (EDMD1; OMIM 310300). The clinical phenotype of this genetic perturbance is manifested in 2nd-3rd decade by contraction of the cervical, elbow and Achilles tendons, by progressive muscle wasting and disturbance of the conduction system and cardiomyopathy, often leading to sudden death. Extensive investigations were made on the functions of this ubiquitous nuclear membrane protein, but the disease causing mechanisms remain obscure leading to the late onset of this tissue specific disease. To allure insights of the pathological function(s) of emerin this work examines the spatio-temporal transcription and expression patterns of emerin during development of the vertebrate model Xenopus laevis. Sequence analysis of EST-databases identified two emerin genes in the pseudo-tetraploid organism Xenopus laevis, Xemerin1 and Xemerin2, respectively. In comparison to the human and murine orthologues Xenopus emerins exhibit both similarities and differences. Structural analyses revealed an N-terminal conserved LEM-domain in the C-terminus and a unique hydrophobic transmembrane domain in the carboxy tail. Unlike the extended mammalian emerin (Homo sapiens 254 residues, Mus musculus 259 residues) neither a nucleus localization signal nor a serinerich region could be detected. However, comparison of the putative phosphorylation sites showed three equivalent sites as for the human emerin. Synthesis of specific monoclonal antibodies and recombinant fusion proteins elucidate the subcellular and tissue-specific localization of Xemerins. Similar to mammalian emerins immunofluorescence microscopy and immunoblotting showed clearly that both Xemerin1 and Xemerin2 are integral nuclear membrane proteins expressing ubiquitously in differentiated cells. Intriguingly, in oocytes Xemerin was undetectable by immunofluorescence and immunoblotting, respectively. Two-dimensional gel electrophoresis NEPHGE proved that our self-made monoclonal antibody 59/7 recognized both Xemerins highlighting two different molecular masses and isoelectric points. Interestingly, Xemerin2 exhibits an increased isoelectric point in 5-days old larvae than in adult somatic culture cells. Immunoblotting of embryonic proteins derived from different developmental stages showed that Xemerin1 and -2 are expressed in stage 43 (Nieuwkoop and Faber, 1975) during Xenopus embryogenesis for the first time. In this context, it is noteworthy that Xenopus A-type lamins – in contrast to previous reports – are already detectable in stage 28. Unexpectedly, RT-PCR analyses proved activity of the Xemerin genes during entire embryogenesis in all stages examined yet. Northern-blotting and sequence analyses of the Xemerin mRNA revealed exceeding untranslated regions with snRNP binding motives. Two independent techniques (band-quantification and quantitative real-time-PCR) bared a significantly increased activity of the Xemerin-genes upon stage 30. Outstanding interest provided the awareness, that exactly at this moment the activity of XMAN1, another inner nuclear membrane protein, was significantly down regulated. Whole mount in situ hybridizations exhibited stressed Xemerin expression in neuro-ectodermal tadpole tissues, as simultaneously reported for XMAN1 (also known as SANE) by to other groups (Osada et al., 2003; Raju et al., 2003). Congruent expression patterns of Xemerin proteins were provided by indirect immunofluorescence of embryonic thin-sections. These results corroborate the theory that XMAN1 and Xemerin could have overlapping functions. At first, recombinant fusion proteins showed an identical subcellular distribution of XMAN1 in comparison with Xemerin. Hence, in vitro binding assays proved direct interaction between Xemerins and XMAN1 as well as with Xenopus A-type lamins. Unfortunately, there is no functional XMAN1 antibody available up to now. Thus, it remains unclear if XMAN1 has overlapping functions with Xemerins during embryogenesis in vivo. Nevertheless, by characterizing Xenopus emerin this work displayed fundamental features for further studies. This opus definitely showed that the model system Xenopus laevis is competitive to the mammalian model ‘mouse’ elucidating the disease causing mechanisms of Emery-Dreifuss muscular dystrophy.

The nuclear lamina consists of a mesh-like network of lamin proteins anchored to the inner nuclear membrane by interactions with integral membrane proteins such as emerin. Emerin binding to lamin A/C is one of the interactions that connect the inner nuclear membrane to the lamina. Infection by herpesviruses results in changes in the organization of the nuclear lamina, perhaps in order to facilitate envelopment of capsids at the inner nuclear membrane. In HSV-1 infected cells, alterations to the lamin proteins have been shown to involve pUL34, pUL31, and pUS3 proteins, which are also required for normal nuclear envelopment. We tested hypotheses about the mechanism and significance of lamina disruption. This thesis presents the following data. Infection of multiple cell types induced emerin hyperphosphorylation that was dependent on the presence of pUL34 and kinase active pUS3 proteins. The pUL34-dependent component was also sensitive to Rottlerin treatment suggesting that cellular kinases sensitive to Rottlerin were involved in emerin modification. LAP2 (another lamin associated protein) was de-modified (perhaps de-phosphorylated) in a pUS3 and pUL34 independent manner. Emerin was not required for growth of HSV-1. Hyperphosphorylation of emerin was required for its disassociation from the lamina. PKC family members have been implicated in the disruption of the nuclear lamina during herpesvirus nuclear egress. To test the hypothesis that PKC activity was required for viral replication, PKC activity was blocked with PKC inhibitors and dominate negative PKC constructs. Chemical inhibition of all PKC isoforms reduced viral growth five-fold and inhibited capsid egress from the nucleus. However, specific inhibition of either conventional PKCs or PKC delta did not inhibit viral growth. In addition to lamin associated proteins, lamin localization is also disrupted during herpesvirus infections. Emerin and lamin A/C are binding partners and the localization of both proteins is disrupted by pUS3 and cellular kinase mediated phosphorylation. To test the hypothesis that HSV-1-induced lamin A/C disruption is mediated via a mechanism similar to emerin's, pUS3 and Rottlerin Sensitive Kinases were inhibited and lamin A/C localization was observed. Unlike emerin, HSV-1-induced disruption of lamin A/C was not altered by Rottlerin Sensitive Kinase inhibition suggesting that HSV has multiple mechanisms for disruption of the lamina. Phosphorylation of lamina components, by Rottlerin Sensitive Kinases, may be a required event prior to primary envelopment. To test this hypothesis, growth of HSV-1 was tested in Rottlerin treated infected cells. Although the inhibitor Rottlerin, did reduce viral growth, it was also was also associated with severe depression of viral late-gene expression. TEM analysis suggested that Rottlerin Sensitive Kinases(s) were required for: (i) nuclear egress and (ii) capsid accumulation or formation supporting the hypothesis that the capsids were made in the presence of Rottlerin were unable to leave the nucleus. pUS3 is a multi-functional protein in alpha-herpesviruses. It has been implicated in lamina disruption, protecting the infected cell from apoptosis, and de-envelopment at the outer nuclear membrane. In BT-549 cells, a breast cancer cell line with low PKC delta expression, the hypothesis was tested that in the absence of cellular lamina disrupting kinases, an US3-null virus would be blocked at the lamina disruption step. In BT-549 cells, the US3-null (vRR1202) virus was 10-fold decreased above the typical 10-fold decrease, compared to WT virus, to produce a 100-fold decrease in infectious PFU yet apoptosis was not increased. Lamin A/C disruption occurred via similar mechanism in both breast cancer cell lines: BT-549 and MCF-7. Interestingly, in the BT-549 cells, emerin was extensively hyperphosphorylated in an US3-null infection, yet was not redistributed along the NE. These data support a model that one or more specific residue(s) must be phosphorylated for emerin disconnection from lamina.

Plusieurs publications, parues lors de ma thèse, ont révélé que les protéines de la membrane nucléaireinterne (INM) et plus particulièrement l’émerine, la lamine A, SUN1, l’actine et BAF, jouaient un rôleessentiel dans les propriétés mécaniques du noyau et de la cellule. L’assemblage de l’enveloppenucléaire et les interactions de ces protéines entre-elles sont régulées par des évènements dephosphorylation et d’oligomérisation. Mon objectif était de décrire les évènements moléculairesessentiels à l’assemblage de l’enveloppe nucléaire interne, afin de pouvoir par la suite comprendrecomment l’enveloppe nucléaire répond à un stress mécanique.J’ai dans un premier temps caractérisé les évènements d’oligomérisation et de phosphorylation de laprotéine émerine. J’ai montré que cette protéine était capable de former, in vitro et en cellules, de grosoligomères indispensables à son interaction avec la lamine A. J’ai également observé que desmutations dans l’émerine, aboutissant à la dystrophie musculaire d’Emery-Dreifuss, affectaient lespropriétés d’auto-association de cette protéine.En parallèle, j’ai étudié les interactions entre émerine, lamine, SUN1, actine et BAF in vitro. J’ai pumontrer des interactions directes entre le domaine C-terminal de la lamine A et les protéines émerine,actine et SUN1. Ces trois protéines lient la lamine A sur des surfaces différentes suggérant l’existencede complexes à 3 ou 4 protéines dans la cellule. L’analyse des modes de régulation des interactionsentre ces protéines doit être poursuivie afin de comprendre quels sont les évènements moléculairesessentiels au maintien de l'intégrité nucléaire et à la transmission d’un signal mécanique entre lecytosquelette et le nucléosquelette. / During my PhD, several papers revealed that the inner nuclear membrane (INM) proteins, andespecially emerin, lamin A, SUN1, actin and BAF, played an essential role in the mechanicalproperties of the nucleus and the cell. The nuclear envelope assembly and the interactions betweenthese proteins are regulated by phosphorylation and oligomerization events. My aim was to describemolecular events essential for inner nuclear envelope assembly as a first step to understand how thenuclear envelope responds to a mechanical stress.I first characterized the oligomerization and phosphorylation states of the protein emerin. I showedthat this protein is capable of forming, in vitro and in cells, large oligomers essential to its interactionwith lamin A. I also observed that several emerin mutations leading to Emery-Dreifuss musculardystrophy impaired the self-association properties of this protein.In parallel, I studied the interactions between emerin, lamin, SUN1, actin and BAF in vitro. I was ableto demonstrate direct interactions between the C-terminal domain of lamin A and the proteins emerin,actin and SUN1. These three proteins bind lamin A on different surfaces suggesting the existence ofcomplexes of 3 or 4 proteins in the cell. Analysis of the mechanisms regulating interactions betweenthese proteins should be pursued in order to understand what are the molecular events responsible forthe maintenance of nuclear integrity and the transmission of a mechanical signal between thecytoskeleton and the nucleoskeleton.

X-Linked Sinus Node Dysfunction and Atrial Fibrillation. Introduction: Atrial fibrillation (AF) is a heritable disorder with male predilection, suggesting a sex chromosome defect in certain patients. Loss-of-function truncation mutations in EMD, encoding the nuclear membrane protein emerin, cause X-linked Emery-Dreifuss muscular dystrophy (EDMD) characterized by localized contractures and skeletal myopathy in adolescence, sinus node dysfunction (SND) in early adulthood, and atrial fibrillation as a variably associated trait. This study sought to identify the genetic basis for male-restricted, nonsyndromic sinus node dysfunction and AF in a multigenerational family. Methods and Results: Genealogical and medical records, and DNA samples, were obtained. Progressive SND and AF occurred in four males related through maternal lineages, consistent with X-linked inheritance. Skeletal myopathy was absent, even at advanced ages. Targeted X chromosome genotyping mapped the disease locus to Xq28, implicating EMD as a positional candidate gene. DNA sequencing revealed hemizygosity for an in-frame 3-bp deletion in EMD (Lys37del) in affected males, disrupting a residue within the LEM binding domain critical for nuclear assembly but leaving the remainder of the protein intact. Buccal epithelial cell staining with emerin antibody demonstrated near-total functional loss of emerin. Female relatives underwent prospective electrocardiographic and genetic testing. Those heterozygous for Lys37del had ∼50-70% emerin-positive nuclei and variable degrees of paroxysmal supraventricular arrhythmia. Conclusions: Mutation of EMD can underlie X-linked familial AF. Lys37del is associated with epithelial cell emerin deficiency, as in EDMD, yet it causes electrical atriomyopathy in the absence of skeletal muscle disease. Targeted genetic testing of EMD should be considered in patients with SND-associated AF and/or family history suggesting X-linked inheritance.

A P56S mutation in the VAPB MSP domain is linked to adult-onset amyotrophic lateral sclerosis 8. The objective of this study is to characterize the functional role of VAPB in transport of NE and NPC proteins from the ER to the NE. Over-expression of VAPB-P56S blocked the transport of nucleoporins (Nups) and NE proteins, resulting in their sequestration in dilated cytoplasmic membranes. Simultaneous overexpression of the FFAT motif (two phenylalanines in an acidic track) antagonizes mutant VAPB effects and restores transport to the NE. VAPB function is required for transport to the NE because knockdown of endogenous VAPB recapitulates this phenotype. Moreover, the compartment in which Nups and NE proteins are sequestered and retained was identified as ER-Golgi intermediate compartment (ERGIC). Moreover, a defect in the transport of NE and NPC proteins attenuates nucleocytoplasmic shuttling of the glucocorticoid receptor (GR). Further, VAPB-P56S which is only soluble in SDS was solubilized in the Triton-X-100 fraction similar to VAPB-WT upon co-transfection with the FFAT motif suggesting that FFAT interacts with the insoluble VAPB-P56S protein changing its biophysical properties.

No description available.

A P56S mutation in the VAPB MSP domain is linked to adult-onset amyotrophic lateral sclerosis 8. The objective of this study is to characterize the functional role of VAPB in transport of NE and NPC proteins from the ER to the NE. Over-expression of VAPB-P56S blocked the transport of nucleoporins (Nups) and NE proteins, resulting in their sequestration in dilated cytoplasmic membranes. Simultaneous overexpression of the FFAT motif (two phenylalanines in an acidic track) antagonizes mutant VAPB effects and restores transport to the NE. VAPB function is required for transport to the NE because knockdown of endogenous VAPB recapitulates this phenotype. Moreover, the compartment in which Nups and NE proteins are sequestered and retained was identified as ER-Golgi intermediate compartment (ERGIC). Moreover, a defect in the transport of NE and NPC proteins attenuates nucleocytoplasmic shuttling of the glucocorticoid receptor (GR). Further, VAPB-P56S which is only soluble in SDS was solubilized in the Triton-X-100 fraction similar to VAPB-WT upon co-transfection with the FFAT motif suggesting that FFAT interacts with the insoluble VAPB-P56S protein changing its biophysical properties.

The nuclear envelope forms the interface between the nucleus and the cytoplasm. The nuclear envelope consists of the two concentric lipid membranes, the nuclear pores and the nuclear lamina. The inner nuclear membrane contains hundreds of unique transmembrane proteins showing high tissue diversity. Mutations of some proteins in the nuclear envelope give rise to a broad spectrum of diseases called envelopathies or laminopathies. In this thesis, I aimed to study the functional organization of the nuclear envelope by identifying and characterizing interactions between the nuclear envelope proteins. For this, we developed a novel method called the Membrane Protein Crosslink Immuno-Precipitation, which enable identification of protein-protein interactions in the nuclear envelope in live cells. We identified several novel interactions of the inner nuclear membrane protein, Samp1, and studied the interaction between the Samp1 and the nuclear GTPase, Ran in detail. Samp1 can bind to Ran and is thus the first known transmembrane Ran binding protein and Samp1 might provide a local binding site for Ran in the inner nuclear membrane. We found that Samp1 also binds to the inner nuclear membrane protein, Emerin and Ran can regulate the Samp1-Emerin interaction in the nuclear envelope. During mitosis, Samp1 distributes in the mitotic spindle. Therefore, we investigated a possible functional role of Samp1 in the mitotic machinery. Samp1 depletion resulted in aneuploid phenotypes, metaphase prolongation and decreased distribution of γ-tubulin and β-tubulin in the mitotic spindle. We found that Samp1 can bind to γ-tubulin, which is essential for the microtubule nucleation and hence for the spindle stability. The new interesting features of Samp1 provide insights on the unforeseen functions of the nuclear envelope proteins. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

A P56S mutation in the VAPB MSP domain is linked to adult-onset amyotrophic lateral sclerosis 8. The objective of this study is to characterize the functional role of VAPB in transport of NE and NPC proteins from the ER to the NE. Over-expression of VAPB-P56S blocked the transport of nucleoporins (Nups) and NE proteins, resulting in their sequestration in dilated cytoplasmic membranes. Simultaneous overexpression of the FFAT motif (two phenylalanines in an acidic track) antagonizes mutant VAPB effects and restores transport to the NE. VAPB function is required for transport to the NE because knockdown of endogenous VAPB recapitulates this phenotype. Moreover, the compartment in which Nups and NE proteins are sequestered and retained was identified as ER-Golgi intermediate compartment (ERGIC). Moreover, a defect in the transport of NE and NPC proteins attenuates nucleocytoplasmic shuttling of the glucocorticoid receptor (GR). Further, VAPB-P56S which is only soluble in SDS was solubilized in the Triton-X-100 fraction similar to VAPB-WT upon co-transfection with the FFAT motif suggesting that FFAT interacts with the insoluble VAPB-P56S protein changing its biophysical properties.