Obscurin

Obscurin, cytoskeletal calmodulin and titin-interacting RhoGEF

PDB rendering based on 1v1c.
Available structures
PDB Ortholog search: PDBe, RCSB
Identifiers
Symbols OBSCN ; ARHGEF30; UNC89
External IDs OMIM: 608616 HomoloGene: 70869 IUPHAR: 2131 GeneCards: OBSCN Gene
EC number 2.7.11.1
Orthologs
Species Human Mouse
Entrez 84033 380698
Ensembl ENSG00000154358 ENSMUSG00000061462
UniProt Q5VST9 A2AAJ9
RefSeq (mRNA) NM_001098623 NM_001003914
RefSeq (protein) NP_001092093 NP_001164983
Location (UCSC) Chr 1:
228.21 – 228.38 Mb		 Chr 11:
58.99 – 59.14 Mb
PubMed search

Obscurin is a protein that in humans is encoded by the OBSCN gene.[1][2][3] Obscurin belongs to the family of giant sacromeric signaling proteins that includes titin and nebulin. Obscurin is expressed in cardiac and skeletal muscle, and plays a role in the organization of myofibrils during sarcomere assembly. A mutation in the OBSCN gene has been associated with hypertrophic cardiomyopathy and altered obscurin protein properties have been associated with other muscle diseases.

Structure

Human obscurin may exist as multiple splice variants of approximately 720 kDa,[4][5][6][7][8] however the full-length nature of only one has been described to date.[9] Obscurin is expressed in cardiac and skeletal muscle. The obscurin gene spans more than 150 kb, contains over 80 exons.[10] The encoded protein contains 68 Ig domains, 2 fibronectin domains, 1 calcium/calmodulin-binding domain, 1 RhoGEF domain with an associated PH domain, and 2 serine-threonine kinase domains.[9] The dominant location of obscurin in mature myofibrils is at the sarcomeric M-band.[9][11] Titin, obscurin, obscurin-like-1 and myomesin form a ternary complex at sarcomeric M-bands that is critical for sarcomere mechanics.[12]

Function

Obscurin belongs to the family of giant sacromeric signaling proteins that includes titin and nebulin, and may have a role in the organization of myofibrils during assembly and may mediate interactions between the sarcoplasmic reticulum and myofibrils. Interestingly, Obscurin is the major cytoplasmic ligand for small ankyrin 1 (sANK1), a sarcoplasmic reticular protein, and the scaffolding function of obscurin appears to prevent degradation of sANK1.[13] These data indicate that obscurin serves as a signaling link between the sarcomeric and sarcoplasmic reticular domains,[14][15] Obscurin plays a role in the formation of new sarcomeres during myofibril assembly.[16] specifically, at the sarcomeric periphery where sites of initiation and progression of myofibrilogenesis lie.[17][18] Obscurin appears to be necessary for the proper incorporation of myosin filaments into sarcomeres and in the assembly of A-bands.[11][19] Moreover, the kinase domains of obscurin are enzymatically active and appear to be involved in the regulation of cell adhesion.[20]

Clinical Significance

Obscurin has been shown to exhibit a disease-related isoform switch in patients with dilated cardiomyopathy.[21] An obscurin mutation Arg4344Gln was identified in patients with hypertrophic cardiomyopathy, which disrupted binding of obscurin to the Z9-Z10 domains of titin.[22] Mutations found the gene encoding titin in patients with limb-girdle muscular dystrophy 2J or Salih myopathy decrease the ability of titin to bind obscurin, suggesting that this may be causative in disease manifestation.[23]

Interactions

Obscurin has been shown to interact with Titin,[1][24] specifically, with the Novex-3 of Titin, a 6.5 kb exon located upstream of the cardiac-specific N2B exon.[25] The C-terminal region of Obscurin interacts with the cytoplasmic domain of small ankyrin 1[26][27] and with the exon 43' region of ankyrin B.[28] The Ig3 of obscurin binds myomesin at the linker between My4 and My5.[23]

References

  1. 1 2 Young P, Ehler E, Gautel M (Jul 2001). "Obscurin, a giant sarcomeric Rho guanine nucleotide exchange factor protein involved in sarcomere assembly". The Journal of Cell Biology 154 (1): 123–36. doi:10.1083/jcb.200102110. PMC 2196875. PMID 11448995.
  2. ↑ Russell MW, Raeker MO, Korytkowski KA, Sonneman KJ (Jan 2002). "Identification, tissue expression and chromosomal localization of human Obscurin-MLCK, a member of the titin and Dbl families of myosin light chain kinases". Gene 282 (1-2): 237–46. doi:10.1016/S0378-1119(01)00795-8. PMID 11814696.
  3. ↑ "Entrez Gene: OBSCN obscurin, cytoskeletal calmodulin and titin-interacting RhoGEF".
  4. ↑ "Q5VST9".
  5. ↑ "Q5VST9-6".
  6. ↑ "Q5VST9-2".
  7. ↑ "Q5VST9-3".
  8. ↑ "Q5VST9-5".
  9. 1 2 3 Young P, Ehler E, Gautel M (Jul 2001). "Obscurin, a giant sarcomeric Rho guanine nucleotide exchange factor protein involved in sarcomere assembly". The Journal of Cell Biology 154 (1): 123–36. doi:10.1083/jcb.200102110. PMC 2196875. PMID 11448995.
  10. ↑ Fukuzawa A, Idowu S, Gautel M (2005). "Complete human gene structure of obscurin: implications for isoform generation by differential splicing". Journal of Muscle Research and Cell Motility 26 (6-8): 427–34. doi:10.1007/s10974-005-9025-6. PMID 16625316.
  11. 1 2 Carlsson L, Yu JG, Thornell LE (Jul 2008). "New aspects of obscurin in human striated muscles". Histochemistry and Cell Biology 130 (1): 91–103. doi:10.1007/s00418-008-0413-z. PMID 18350308.
  12. ↑ Pernigo S, Fukuzawa A, Bertz M, Holt M, Rief M, Steiner RA, Gautel M (Feb 2010). "Structural insight into M-band assembly and mechanics from the titin-obscurin-like-1 complex". Proceedings of the National Academy of Sciences of the United States of America 107 (7): 2908–13. doi:10.1073/pnas.0913736107. PMID 20133654.
  13. ↑ Lange S, Perera S, Teh P, Chen J (Jul 2012). "Obscurin and KCTD6 regulate cullin-dependent small ankyrin-1 (sAnk1.5) protein turnover". Molecular Biology of the Cell 23 (13): 2490–504. doi:10.1091/mbc.E12-01-0052. PMID 22573887.
  14. ↑ Bagnato P, Barone V, Giacomello E, Rossi D, Sorrentino V (Jan 2003). "Binding of an ankyrin-1 isoform to obscurin suggests a molecular link between the sarcoplasmic reticulum and myofibrils in striated muscles". The Journal of Cell Biology 160 (2): 245–53. doi:10.1083/jcb.200208109. PMC 2172649. PMID 12527750.
  15. ↑ Kontrogianni-Konstantopoulos A, Jones EM, Van Rossum DB, Bloch RJ (Mar 2003). "Obscurin is a ligand for small ankyrin 1 in skeletal muscle". Molecular Biology of the Cell 14 (3): 1138–48. doi:10.1091/mbc.E02-07-0411. PMC 151585. PMID 12631729.
  16. ↑ Borisov AB, Kontrogianni-Konstantopoulos A, Bloch RJ, Westfall MV, Russell MW (Sep 2004). "Dynamics of obscurin localization during differentiation and remodeling of cardiac myocytes: obscurin as an integrator of myofibrillar structure". The Journal of Histochemistry and Cytochemistry 52 (9): 1117–27. doi:10.1369/jhc.3A6183.2004. PMID 15314079.
  17. ↑ Borisov AB, Raeker MO, Kontrogianni-Konstantopoulos A, Yang K, Kurnit DM, Bloch RJ, Russell MW (Oct 2003). "Rapid response of cardiac obscurin gene cluster to aortic stenosis: differential activation of Rho-GEF and MLCK and involvement in hypertrophic growth". Biochemical and Biophysical Research Communications 310 (3): 910–8. doi:10.1016/j.bbrc.2003.09.035. PMID 14550291.
  18. ↑ Borisov AB, Martynova MG, Russell MW (Apr 2008). "Early incorporation of obscurin into nascent sarcomeres: implication for myofibril assembly during cardiac myogenesis". Histochemistry and Cell Biology 129 (4): 463–78. doi:10.1007/s00418-008-0378-y. PMID 18219491.
  19. ↑ Borisov AB, Sutter SB, Kontrogianni-Konstantopoulos A, Bloch RJ, Westfall MV, Russell MW (Mar 2006). "Essential role of obscurin in cardiac myofibrillogenesis and hypertrophic response: evidence from small interfering RNA-mediated gene silencing". Histochemistry and Cell Biology 125 (3): 227–38. doi:10.1007/s00418-005-0069-x. PMID 16205939.
  20. ↑ Hu LY, Kontrogianni-Konstantopoulos A (May 2013). "The kinase domains of obscurin interact with intercellular adhesion proteins". FASEB Journal 27 (5): 2001–12. doi:10.1096/fj.12-221317. PMID 23392350.
  21. ↑ Makarenko I, Opitz CA, Leake MC, Neagoe C, Kulke M, Gwathmey JK, del Monte F, Hajjar RJ, Linke WA (Oct 2004). "Passive stiffness changes caused by upregulation of compliant titin isoforms in human dilated cardiomyopathy hearts". Circulation Research 95 (7): 708–16. doi:10.1161/01.RES.0000143901.37063.2f. PMID 15345656.
  22. ↑ Arimura T, Matsumoto Y, Okazaki O, Hayashi T, Takahashi M, Inagaki N, Hinohara K, Ashizawa N, Yano K, Kimura A (Oct 2007). "Structural analysis of obscurin gene in hypertrophic cardiomyopathy". Biochemical and Biophysical Research Communications 362 (2): 281–7. doi:10.1016/j.bbrc.2007.07.183. PMID 17716621.
  23. 1 2 Fukuzawa A, Lange S, Holt M, Vihola A, Carmignac V, Ferreiro A, Udd B, Gautel M (Jun 2008). "Interactions with titin and myomesin target obscurin and obscurin-like 1 to the M-band: implications for hereditary myopathies". Journal of Cell Science 121 (Pt 11): 1841–51. doi:10.1242/jcs.028019. PMID 18477606.
  24. ↑ Pernigo S, Fukuzawa A, Pandini A, Holt M, Kleinjung J, Gautel M, Steiner RA (Feb 2015). "The crystal structure of the human titin:obscurin complex reveals a conserved yet specific muscle M-band zipper module". Journal of Molecular Biology 427 (4): 718–36. doi:10.1016/j.jmb.2014.11.019. PMID 25490259.
  25. ↑ Bang ML, Centner T, Fornoff F, Geach AJ, Gotthardt M, McNabb M, Witt CC, Labeit D, Gregorio CC, Granzier H, Labeit S (Nov 2001). "The complete gene sequence of titin, expression of an unusual approximately 700-kDa titin isoform, and its interaction with obscurin identify a novel Z-line to I-band linking system". Circulation Research 89 (11): 1065–72. doi:10.1161/hh2301.100981. PMID 11717165.
  26. ↑ Kontrogianni-Konstantopoulos A, Jones EM, Van Rossum DB, Bloch RJ (Mar 2003). "Obscurin is a ligand for small ankyrin 1 in skeletal muscle". Molecular Biology of the Cell 14 (3): 1138–48. doi:10.1091/mbc.E02-07-0411. PMC 151585. PMID 12631729.
  27. ↑ Busby B, Oashi T, Willis CD, Ackermann MA, Kontrogianni-Konstantopoulos A, Mackerell AD, Bloch RJ (Apr 2011). "Electrostatic interactions mediate binding of obscurin to small ankyrin 1: biochemical and molecular modeling studies". Journal of Molecular Biology 408 (2): 321–34. doi:10.1016/j.jmb.2011.01.053. PMID 21333652.
  28. ↑ Cunha SR, Mohler PJ (Nov 2008). "Obscurin targets ankyrin-B and protein phosphatase 2A to the cardiac M-line". The Journal of Biological Chemistry 283 (46): 31968–80. doi:10.1074/jbc.M806050200. PMID 18782775.

Further reading

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