Gamma-actin is a protein that in humans is encoded by the ACTG1gene.[1] Gamma-actin is widely expressed in cellular cytoskeletons of many tissues; in adult striated muscle cells, gamma-actin is localized to Z-discs and costamere structures, which are responsible for force transduction and transmission in muscle cells. Mutations in ACTG1 have been associated with nonsyndromic hearing loss and Baraitser-Winter syndrome, as well as susceptibility of adolescent patients to vincristine toxicity.
Human gamma-actin is 41.8 kDa in molecular weight and 375 amino acids in length.[2] Actins are highly conserved proteins that are involved in various types of cell motility, and maintenance of the cytoskeleton. In vertebrates, three main groups of actin isoforms, alpha, beta and gamma have been identified.[3]
The alpha actins are found in muscle tissues and are a major constituent of the sarcomere contractile apparatus. The beta and gamma actins co-exist in most cell types as components of the cytoskeleton, and as mediators of internal cell motility. Actin, gamma 1, encoded by this gene, is found in non-muscle cells in the cytoplasm, and in muscle cells at costamere structures, or transverse points of cell-cell adhesion that run perpendicular to the long axis of myocytes.[4][5][6]
Insights into the function of gamma-actin in muscle have come from studies employing transgenesis. In a skeletal muscle-specific knockout of gamma-actin in mice, these animals showed no detectable abnormalities in development; however, knockout mice showed muscle weakness and fiber necrosis, along with decreased isometric twitch force, disrupted intrafibrillar and interfibrillar connections among myocytes, and myopathy.[20]
Clinical Significance
An autosomal dominant mutation in ACTG1 in the DFNA20/26 locus at 17q25-qter was identified in patients with hearing loss. A Thr278Ile mutation was identified in helix 9 of gamma-actin protein, which is predicted to alter protein structure. This study identified the first disease causing mutation in gamma-actin and underlies the importance of gamma-actin as structural elements of the inner ear hair cells.[21] Since then, other ACTG1 mutations have been linked to nonsyndromic hearing loss, including Met305Thr.[22]
↑Clark KA, McElhinny AS, Beckerle MC, Gregorio CC (2002). "Striated muscle cytoarchitecture: an intricate web of form and function". Annual Review of Cell and Developmental Biology. 18: 637–706. doi:10.1146/annurev.cellbio.18.012502.105840. PMID12142273.
↑Kee AJ, Gunning PW, Hardeman EC (2009). "Diverse roles of the actin cytoskeleton in striated muscle". Journal of Muscle Research and Cell Motility. 30 (5–6): 187–97. doi:10.1007/s10974-009-9193-x. PMID19997772.
↑Ervasti JM (Apr 2003). "Costameres: the Achilles' heel of Herculean muscle". The Journal of Biological Chemistry. 278 (16): 13591–4. doi:10.1074/jbc.R200021200. PMID12556452.
↑ 11.011.1Nakata T, Nishina Y, Yorifuji H (Aug 2001). "Cytoplasmic gamma actin as a Z-disc protein". Biochemical and Biophysical Research Communications. 286 (1): 156–63. doi:10.1006/bbrc.2001.5353. PMID11485322.
↑Papponen H, Kaisto T, Leinonen S, Kaakinen M, Metsikkö K (Jan 2009). "Evidence for gamma-actin as a Z disc component in skeletal myofibers". Experimental Cell Research. 315 (2): 218–25. doi:10.1016/j.yexcr.2008.10.021. PMID19013151.
↑Lloyd CM, Berendse M, Lloyd DG, Schevzov G, Grounds MD (Jul 2004). "A novel role for non-muscle gamma-actin in skeletal muscle sarcomere assembly". Experimental Cell Research. 297 (1): 82–96. doi:10.1016/j.yexcr.2004.02.012. PMID15194427.
↑Schwartz RJ, Rothblum KN (Jul 1981). "Gene switching in myogenesis: differential expression of the chicken actin multigene family". Biochemistry. 20 (14): 4122–9. doi:10.1021/bi00517a027. PMID7284314.
↑Shani M, Zevin-Sonkin D, Saxel O, Carmon Y, Katcoff D, Nudel U, Yaffe D (Sep 1981). "The correlation between the synthesis of skeletal muscle actin, myosin heavy chain, and myosin light chain and the accumulation of corresponding mRNA sequences during myogenesis". Developmental Biology. 86 (2): 483–92. doi:10.1016/0012-1606(81)90206-2. PMID7286410.
↑Sonnemann KJ, Fitzsimons DP, Patel JR, Liu Y, Schneider MF, Moss RL, Ervasti JM (Sep 2006). "Cytoplasmic gamma-actin is not required for skeletal muscle development but its absence leads to a progressive myopathy". Developmental Cell. 11 (3): 387–97. doi:10.1016/j.devcel.2006.07.001. PMID16950128.
↑Hertzog M, van Heijenoort C, Didry D, Gaudier M, Coutant J, Gigant B, Didelot G, Préat T, Knossow M, Guittet E, Carlier MF (May 2004). "The beta-thymosin/WH2 domain; structural basis for the switch from inhibition to promotion of actin assembly". Cell. 117 (5): 611–23. doi:10.1016/S0092-8674(04)00403-9. PMID15163409.
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1dej: CRYSTAL STRUCTURE OF A DICTYOSTELIUM/TETRAHYMENA CHIMERA ACTIN (MUTANT 646: Q228K/T229A/A230Y/A231K/S232E/E360H) IN COMPLEX WITH HUMAN GELSOLIN SEGMENT 1