Nebulin Explained

Nebulin^[1] is an actin-binding protein which is localized to the thin filament of the sarcomeres in skeletal muscle. Nebulin in humans is coded for by the gene NEB. It is a very large protein (600–900 kDa) and binds as many as 200 actin monomers. Because its length is proportional to thin filament length, it is believed that nebulin acts as a thin filament "ruler" and regulates thin filament length during sarcomere assembly.^[2] Other functions of nebulin, such as a role in cell signaling, remain uncertain.

Nebulin has also been shown to regulate actin-myosin interactions by inhibiting ATPase activity in a calcium-calmodulin sensitive manner.^[3]

Mutations in nebulin cause some cases of the autosomal recessive disorder nemaline myopathy.^[4]

A smaller member of the nebulin protein family, termed nebulette, is expressed in cardiac muscle.

Structure

The structure of the SH3 domain of nebulin was determined by protein nuclear magnetic resonance spectroscopy.^[5] The SH3 domain from nebulin is composed of 60 amino acid residues, of which 30 percent is in the beta sheet secondary structure (7 strands; 18 residues).

Knockout phenotype

As of 2007, two knockout mouse models for nebulin have been developed to better understand its in vivo function. Bang and colleagues^[6] demonstrated that nebulin-knockout mice die postnatally, have reduced thin filament length, and impaired contractile function. Postnatal sarcomere disorganization and degeneration occurred rapidly in these mice, indicating the nebulin is essential for maintaining the structural integrity of myofibrils. Witt and colleagues^[7] had similar results in their mice, which also died postnatally with reduced thin filament length and contractile function. These nebulin-knockout mice are being investigated as animal models of nemaline myopathy.

Further reading

• Björklund AK, Light S, Sagit R, Elofsson A . Nebulin: a study of protein repeat evolution . Journal of Molecular Biology . 402 . 1 . 38–51 . September 2010 . 20643138 . 10.1016/j.jmb.2010.07.011 .

External links

• • GeneReviews/NCBI/NIH/UW entry on Nemaline Myopathy
• PDBe-KB provides an overview of all the structure information available in the PDB for Human Nebulin

Notes and References

1. Wang. K.. Williamson. C. L.. June 1980. Identification of an N2 line protein of striated muscle. Proceedings of the National Academy of Sciences of the United States of America. 77. 6. 3254–3258. 10.1073/pnas.77.6.3254. 0027-8424. 349593. 6997874. 1980PNAS...77.3254W . free .
2. McElhinny AS, Kazmierski ST, Labeit S, Gregorio CC . Nebulin: the nebulous, multifunctional giant of striated muscle . Trends in Cardiovascular Medicine . 13 . 5 . 195–201 . July 2003 . 12837582 . 10.1016/S1050-1738(03)00076-8 .
3. Root DD, Wang K . Calmodulin-sensitive interaction of human nebulin fragments with actin and myosin . Biochemistry . 33 . 42 . 12581–91 . October 1994 . 7918483 . 10.1021/bi00208a008 .
4. Pelin K, Hilpelä P, Donner K, Sewry C, Akkari PA, Wilton SD, Wattanasirichaigoon D, Bang ML, Centner T, Hanefeld F, Odent S, Fardeau M, Urtizberea JA, Muntoni F, Dubowitz V, Beggs AH, Laing NG, Labeit S, de la Chapelle A, Wallgren-Pettersson C . Mutations in the nebulin gene associated with autosomal recessive nemaline myopathy . Proceedings of the National Academy of Sciences of the United States of America . 96 . 5 . 2305–10 . March 1999 . 10051637 . 26779 . 10.1073/pnas.96.5.2305 . 1999PNAS...96.2305P . free .

5. Politou AS, Millevoi S, Gautel M, Kolmerer B, Pastore A . SH3 in muscles: solution structure of the SH3 domain from nebulin . J. Mol. Biol. . 276 . 1 . 189–202 . February 1998 . 9514727 . 10.1006/jmbi.1997.1521 .

6. Bang ML, Li X, Littlefield R, Bremner S, Thor A, Knowlton KU, Lieber RL, Chen J . Nebulin-deficient mice exhibit shorter thin filament lengths and reduced contractile function in skeletal muscle . The Journal of Cell Biology . 173 . 6 . 905–16 . Jun 2006 . 16769824 . 2063916 . 10.1083/jcb.200603119 .
7. Witt CC, Burkart C, Labeit D, McNabb M, Wu Y, Granzier H, Labeit S . Nebulin regulates thin filament length, contractility, and Z-disk structure in vivo . The EMBO Journal . 25 . 16 . 3843–55 . August 2006 . 16902413 . 1553189 . 10.1038/sj.emboj.7601242 .