Emerin is a protein that in humans is encoded by the EMD gene, also known as the STA gene. Emerin, together with LEMD3, is a LEM domain-containing integral protein of the inner nuclear membrane in vertebrates. Emerin is highly expressed in cardiac and skeletal muscle. In cardiac muscle, emerin localizes to adherens junctions within intercalated discs where it appears to function in mechanotransduction of cellular strain and in beta-catenin signaling. Mutations in emerin cause X-linked recessive Emery–Dreifuss muscular dystrophy, cardiac conduction abnormalities and dilated cardiomyopathy.
It is named after Alan Emery. [5]
Emerin is a 29.0 kDa (34 kDa observed MW) protein composed of 254 amino acids. [6] Emerin is a serine-rich protein with an N-terminal 20-amino acid hydrophobic region that is flanked by charged residues; the hydrophobic region may be important for anchoring the protein to the membrane, with the charged terminal tails being cytosolic. [7] In cardiac, skeletal, and smooth muscle, emerin localizes to the inner nuclear membrane; [8] [9] expression of emerin is highest in skeletal and cardiac muscle. [7] In cardiac muscle specifically, emerin also resides at adherens junctions within intercalated discs. [10] [11] [12]
Emerin is a serine-rich nuclear membrane protein and a member of the nuclear lamina-associated protein family. It mediates membrane anchorage to the cytoskeleton. Emery–Dreifuss muscular dystrophy is an X-linked inherited degenerative myopathy resulting from mutation in the EMD (also known clinically as STA) gene. [13] Emerin appears to be involved in mechanotransduction, as emerin-deficient mouse fibroblasts failed to transduce normal mechanosensitive gene expression responses to strain stimuli. [14] In cardiac muscle, emerin is also found complexed to beta-catenin at adherens junctions of intercalated discs, and cardiomyocytes from hearts lacking emerin showed beta-catenin redistribution as well as perturbed intercalated disc architecture and myocyte shape. This interaction appears to be regulated by glycogen synthase kinase 3 beta. [15]
Mutations in emerin cause X-linked recessive Emery–Dreifuss muscular dystrophy, which is characterized by early contractures in the Achilles tendons, elbows and post-cervical muscles; muscle weakness proximal in the upper limbs and distal in lower limbs; along with cardiac conduction defects that range from sinus bradycardia, PR prolongation to complete heart block. [16] In these patients, immunostaining of emerin is lost in various tissues, including muscle, skin fibroblasts, and leukocytes, however diagnostic protocols involve mutational analysis rather than protein staining. [16] In nearly all cases, mutations result in a complete deletion, or undetectable levels, of emerin protein. Approximately 20% of cases have X chromosomes with an inversion within the Xq28 region. [17]
Moreover, recent research have found that the absence of functional emerin may decrease the infectivity of HIV-1. Thus, it is speculated that patients with Emery–Dreifuss muscular dystrophy may have immunity to or show an irregular infection pattern to HIV-1. [18]
Emerin has been shown to interact with:
Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily affected, the degree of weakness, how fast they worsen, and when symptoms begin. Some types are also associated with problems in other organs.
Plectin is a giant protein found in nearly all mammalian cells which acts as a link between the three main components of the cytoskeleton: actin microfilaments, microtubules and intermediate filaments. In addition, plectin links the cytoskeleton to junctions found in the plasma membrane that structurally connect different cells. By holding these different networks together, plectin plays an important role in maintaining the mechanical integrity and viscoelastic properties of tissues.
Dysferlin also known as dystrophy-associated fer-1-like protein is a protein that in humans is encoded by the DYSF gene. Dysferlin is linked with plasma membrane repair., stabilization of calcium signaling and the development of the T-tubule system of the muscle A defect in the DYSF gene, located on chromosome 2p12-14, results in several types of muscular dystrophy; including Miyoshi myopathy (MM), Limb-girdle muscular dystrophy type 2B (LGMD2B) and Distal Myopathy (DM). A reduction or absence of dysferlin, termed dysferlinopathy, usually becomes apparent in the third or fourth decade of life and is characterised by weakness and wasting of various voluntary skeletal muscles. Pathogenic mutations leading to dysferlinopathy can occur throughout the DYSF gene.
Catenin beta-1, also known as β-catenin (beta-catenin), is a protein that in humans is encoded by the CTNNB1 gene.
Emery–Dreifuss muscular dystrophy (EDMD) is a type of muscular dystrophy, a group of heritable diseases that cause progressive impairment of muscles. EDMD affects muscles used for movement, causing atrophy, weakness and contractures. It almost always affects the heart, causing abnormal rhythms, heart failure, or sudden cardiac death. It is rare, affecting 0.39 per 100,000 people. It is named after Alan Eglin H. Emery and Fritz E. Dreifuss.
Plakoglobin, also known as junction plakoglobin or gamma-catenin, is a protein that in humans is encoded by the JUP gene. Plakoglobin is a member of the catenin protein family and homologous to β-catenin. Plakoglobin is a cytoplasmic component of desmosomes and adherens junctions structures located within intercalated discs of cardiac muscle that function to anchor sarcomeres and join adjacent cells in cardiac muscle. Mutations in plakoglobin are associated with arrhythmogenic right ventricular dysplasia.
Laminopathies are a group of rare genetic disorders caused by mutations in genes encoding proteins of the nuclear lamina. Since the first reports of laminopathies in the late 1990s, increased research efforts have started to uncover the vital role of nuclear envelope proteins in cell and tissue integrity in animals. Laminopathies are a group of degenerative diseases, other disorders associated with inner nuclear membrane proteins are known as nuclear envelopathies.
Prelamin-A/C, or lamin A/C is a protein that in humans is encoded by the LMNA gene. Lamin A/C belongs to the lamin family of proteins.
Sarcospan is a protein that in humans is encoded by the SSPN gene.
Alpha-7 integrin is a protein that in humans is encoded by the ITGA7 gene. Alpha-7 integrin is critical for modulating cell-matrix interactions. Alpha-7 integrin is highly expressed in cardiac muscle, skeletal muscle and smooth muscle cells, and localizes to Z-disc and costamere structures. Mutations in ITGA7 have been associated with congenital myopathies and noncompaction cardiomyopathy, and altered expression levels of alpha-7 integrin have been identified in various forms of muscular dystrophy.
Myotilin is a protein that in humans is encoded by the MYOT gene. Myotilin also known as TTID is a muscle protein that is found within the Z-disc of sarcomeres.
Gamma-sarcoglycan is a protein that in humans is encoded by the SGCG gene. The α to δ-sarcoglycans are expressed predominantly (β) or exclusively in striated muscle. A mutation in any of the sarcoglycan genes may lead to a secondary deficiency of the other sarcoglycan proteins, presumably due to destabilisation of the sarcoglycan complex. The disease-causing mutations in the α to δ genes cause disruptions within the dystrophin-associated protein (DAP) complex in the muscle cell membrane. The transmembrane components of the DAP complex link the cytoskeleton to the extracellular matrix in adult muscle fibres, and are essential for the preservation of the integrity of the muscle cell membrane.
Nesprin-2 is a protein that in humans is encoded by the SYNE2 gene. The human SYNE2 gene consists of 116 exons and encodes nesprin-2, a member of the nuclear envelope (NE) spectrin-repeat (nesprin) family. Nesprins are modular proteins with a central extended spectrin-repeat (SR) rod domain and a C-terminal Klarsicht/ANC-1/Syne homology (KASH) transmembrane domain, which acts as a NE-targeting motif. Nesprin-2 (Nesp2) binds to cytoplasmic F-actin, tethering the nucleus to the cytoskeleton and maintaining the structural integrity of the nucleus.
Cysteine and glycine-rich protein 3 also known as cardiac LIM protein (CLP) or muscle LIM protein (MLP) is a protein that in humans is encoded by the CSRP3 gene.
Bcl-2-associated transcription factor 1 is a Bcl-2 family protein in humans that is encoded by the BCLAF1 gene.
Transmembrane protein 43 is a protein that in humans is encoded by the TMEM43 gene. TMEM43 may have an important role in maintaining nuclear envelope structure by organizing protein complexes at the inner nuclear membrane. Required for retaining emerin at the inner nuclear membrane. However, the localization of TMEM43 in myocardial tissue is controversial discussed. Franke et al. demonstrated that TMEM43 is localized at the intercalated disc but not at the nuclear envelope. In contrast Christensen et al. have shown that TMEM43 is mainly localized at the sarcolemma. Mutations in TMEM43 are associated with ARVD and EDMD7.
Torsin-1A-interacting protein 1 is a protein that in humans is encoded by the TOR1AIP1 gene. More commonly known as lamina associated polypeptide 1 (LAP1), it is a type II integral membrane protein that resides in the inner nuclear membrane. The luminal domain of LAP1 interacts with Torsin A and is necessary for the ATPase activity of Torsin A. LAP1 plays a critical role in skeletal and heart muscle. Mutations in TOR1AIP1 have been linked to muscular dystrophy and cardiomyopathy. It's deletion from mouse hepatocytes leads to defected very-low density lipoprotein secretion and causes non-alcoholic fatty liver disease and non-alcoholic steatohepatitis
αE-catenin, also known as Catenin alpha-1 is a protein that in humans is encoded by the CTNNA1 gene. αE-catenin is highly expressed in cardiac muscle and localizes to adherens junctions at intercalated disc structures where it functions to mediate the anchorage of actin filaments to the sarcolemma. αE-catenin also plays a role in tumor metastasis and skin cell function.
Inner nuclear membrane proteins are membrane proteins that are embedded in or associated with the inner membrane of the nuclear envelope. There are about 60 INM proteins, most of which are poorly characterized with respect to structure and function. Among the few well-characterized INM proteins are lamin B receptor (LBR), lamina-associated polypeptide 1 (LAP1), lamina-associated polypeptide-2 (LAP2), emerin and MAN1.
Lamin A/C congenital muscular dystrophy (CMD) is a disease that it is included in laminopathies. Laminopathies are caused, among other mutations, to mutations in LMNA, a gene that synthesizes lamins A and C.
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