Biology:SGCG

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A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example

Gamma-sarcoglycan is a protein that in humans is encoded by the SGCG gene.[1][2] The α to δ-sarcoglycans are expressed predominantly (β) or exclusively (α, γ and δ) in striated muscle.[3] 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.[4] The disease-causing mutations in the α to δ genes cause disruptions within the dystrophin-associated protein (DAP) complex in the muscle cell membrane.[5] The transmembrane components of the DAP complex link the cytoskeleton to the extracellular matrix in adult muscle fibres,[6] and are essential for the preservation of the integrity of the muscle cell membrane.[7]

Function

Gamma-sarcoglycan is one of several sarcolemmal transmembrane glycoproteins that interact with dystrophin, probably to provide a link between the membrane associated cytoskeleton and the extracellular matrix. Defects in the protein can lead to early onset autosomal recessive muscular dystrophy, in particular limb-girdle muscular dystrophy, type 2C (LGMD2C).[2]

Structure

Gene

Human SGCG gene maps to chromosome 13 at q12, spans over 100 kb of DNA and includes 8 exons.[8]

Protein

Gamma-sarcoglycan is a type II transmembrane protein and consists of 291 amino acids. It has a 35 amino acid intracellular N-terminal region, a 25 amino acid single transmembrane domain, and a 231 amino acid extra-cellular C-terminus.[4]

Clinical significance

Sarcoglycanopathies are autosomal recessive limb girdle muscular dystrophies (LGMDs) caused by mutations in any of the four sarcoglycan genes: α (LGMD2D), β (LGMD2E), γ (LGMD2C) and δ (LGMD2F).[3] Severe childhood autosomal recessive muscular dystrophy (SCARMD) is a progressive muscle-wasting disorder that segregates with microsatellite markers at γ-sarcoglycan gene. Mutations in the γ-sarcoglycan gene were first described in the Maghreb countries of North Africa,[9] where γ-sarcoglycanopathy has a higher than usual incidence. One common mutation, Δ-521T, which causes a severe phenotype, occurs both in the Maghreb population and in other countries.[8] A Cys283Tyr mutation has been identified in the Gypsy population causing a severe phenotype and a Leu193Ser mutation which causes a mild phenotype.[1][10]

Interactions

SGCG has been shown to interact with FLNC.[11][12]

References

  1. 1.0 1.1 "A founder mutation in the gamma-sarcoglycan gene of gypsies possibly predating their migration out of India". Human Molecular Genetics 5 (12): 2019–22. Dec 1996. doi:10.1093/hmg/5.12.2019. PMID 8968757. 
  2. 2.0 2.1 "Entrez Gene: SGCG sarcoglycan, gamma (35kDa dystrophin-associated glycoprotein)". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=6445. 
  3. 3.0 3.1 "Mutations in the dystrophin-associated protein gamma-sarcoglycan in chromosome 13 muscular dystrophy". Science 270 (5237): 819–22. Nov 1995. doi:10.1126/science.270.5237.819. PMID 7481775. Bibcode1995Sci...270..819N. 
  4. 4.0 4.1 "Severe gamma-sarcoglycanopathy caused by a novel missense mutation and a large deletion". Neuromuscular Disorders 10 (2): 100–7. Feb 2000. doi:10.1016/s0960-8966(99)00063-2. PMID 10714584. 
  5. "The sarcoglycan complex in the six autosomal recessive limb-girdle muscular dystrophies". Human Molecular Genetics 5 (12): 1963–9. Dec 1996. doi:10.1093/hmg/5.12.1963. PMID 8968750. 
  6. "epsilon-Sarcoglycan, a broadly expressed homologue of the gene mutated in limb-girdle muscular dystrophy 2D". The Journal of Biological Chemistry 272 (51): 32534–8. Dec 1997. doi:10.1074/jbc.272.51.32534. PMID 9405466. 
  7. "Assembly of the sarcoglycan complex. Insights for muscular dystrophy". The Journal of Biological Chemistry 273 (52): 34667–70. Dec 1998. doi:10.1074/jbc.273.52.34667. PMID 9856984. 
  8. 8.0 8.1 "Mutations that disrupt the carboxyl-terminus of gamma-sarcoglycan cause muscular dystrophy". Human Molecular Genetics 5 (11): 1841–7. Nov 1996. doi:10.1093/hmg/5.11.1841. PMID 8923014. 
  9. "Linkage analysis of families with severe childhood autosomal recessive muscular dystrophy in Morocco indicates genetic homogeneity of the disease in north Africa". Journal of Medical Genetics 31 (4): 342–3. Apr 1994. doi:10.1136/jmg.31.4.342. PMID 8071965. 
  10. "A novel gamma-sarcoglycan mutation causing childhood onset, slowly progressive limb girdle muscular dystrophy". Neuromuscular Disorders 8 (5): 305–8. Jun 1998. doi:10.1016/s0960-8966(98)00040-6. PMID 9673983. 
  11. "Calpain 3 cleaves filamin C and regulates its ability to interact with gamma- and delta-sarcoglycans". Muscle Nerve 28 (4): 472–83. October 2003. doi:10.1002/mus.10465. PMID 14506720. 
  12. "Filamin 2 (FLN2): A muscle-specific sarcoglycan interacting protein". J. Cell Biol. 148 (1): 115–26. January 2000. doi:10.1083/jcb.148.1.115. PMID 10629222. 

Further reading

External links

  • LOVD mutation database: SGCG