MYL4

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Protein-coding gene in the species Homo sapiens

title: "MYL4" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public description: "Protein-coding gene in the species Homo sapiens" topic_path: "uncategorized" source: "https://en.wikipedia.org/wiki/MYL4" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Protein-coding gene in the species Homo sapiens ::

Atrial Light Chain-1 (ALC-1), also known as Essential Light Chain, Atrial is a protein that in humans is encoded by the MYL4 gene. ALC-1 is expressed in fetal cardiac ventricular and fetal skeletal muscle, as well as fetal and adult cardiac atrial tissue. ALC-1 expression is reactivated in human ventricular myocardium in various cardiac muscle diseases, including hypertrophic cardiomyopathy, dilated cardiomyopathy, ischemic cardiomyopathy and congenital heart diseases.

Structure

ALC-1 is a 21.6 kDa protein composed of 197 amino acids. ALC-1 is expressed in fetal cardiac ventricular and fetal skeletal muscle, as well as fetal and adult cardiac atrial tissue. ALC-1 binds the neck region of muscle myosin in adult atria. Two alternatively spliced transcript variants encoding the same protein have been found for this gene. Relative to ventricular essential light chain VLC-1, ALC-1 has an additional ~40 amino-acid N-terminal region that contains four to eleven residues that are critical for binding actin and modulating myosin kinetics.

Function

ALC-1 is expressed very early in skeletal muscle and cardiac muscle development; two E-boxes and CArG box in the MYL4 promoter region regulate transcription. ALC-1 expression in cardiac ventricles decreases in early postnatal development, but is highly expressed in atria throughout all of adulthood. Normal atrial function is essential for embryogenesis, as inactivation of the MYL7 gene was embryonic lethal at ED10.5-11.5.

Evidence of ALC-1 isoform expression on contractile mechanics of sarcomeres came from experiments studying fibers from patients expressing a higher level of ALC-1 relative to VLC-1 in cardiac left ventricular tissue. Fibers expressing high ALC-1 exhibited a higher maximal velocity and rate of shortening compared to fibers with low amounts of ALC-1, suggesting that ALC-1 increases cycling kinetics of myosin cross-bridges and regulates cardiac contractility. Further biochemical studies unveiled a weaker binding of the Alanine-Proline-rich N-terminus of ALC-1 to the C-terminus of actin relative to VLC-1, which may explain the mechanism underlying the differences in cycling kinetics. The importance of this region has however raised skepticism. Further evidence for the contractile-enhancing properties of ALC-1 came from studies employing transgenesis to replace VLC-1 with ALC-1 in the mouse ventricle. This study demonstrated an increase in unloaded shortening velocity, both in skinned fibers and in an in vitro motility assay, as well as enhanced contractility and relaxation in whole heart experiments. These studies were supported by further studies in transgenic rats overexpressing ALC-1 which showed enhanced rates of contraction and relaxation, as well as left ventricular developed pressure in Langendorff heart preparations. Importantly, overexpression of ALC-1 was shown to attenuate heart failure in pressure-overloaded animals, by enhancing left ventricular developed pressure, maximal velocity of pressure development and relaxation.

Clinical significance

MYL4 expression in ventricular myocardium has shown to abnormally persist in neonates up through adulthood in patients with the congenital heart disease, tetralogy of Fallot. Altered ALC-1 expression is also altered in other congenital heart diseases, Double outlet right ventricle and infundibular pulmonary stenosis. Moreover, in patients with aortic stenosis or aortic insufficiency, ALC-1 expression in left ventricles was elevated, and following valve replacement decreased to lower levels; ALC-1 expression also correlated with left ventricular systolic pressure.

Additionally, in patients with ischemic cardiomyopathy, dilated cardiomyopathy and hypertrophic cardiomyopathy, ALC-1 protein expression is shown to be reactivated, and ALC-1 expression correlates with calcium sensitivity of myofilament proteins in skinned fiber preparations, as well as ventricular dP/dtmax and ejection fraction.

Interactions

ALC-1 interacts with:

References

References

  1. (September 1988). "Molecular cloning and characterization of human atrial and ventricular myosin alkali light chain cDNA clones". The Journal of Biological Chemistry.
  2. "Entrez Gene: MYL4 myosin, light chain 4, alkali; atrial, embryonic".
  3. "Protein sequence of human MYL4 (Uniprot ID: P12829)".
  4. (February 1990). "Heterogenic mRNAs with an identical protein-coding region of the human embryonic myosin alkali light chain in skeletal muscle cells". Journal of Molecular Biology.
  5. (August 1998). "The N-terminus of A1-type myosin essential light chains binds actin and modulates myosin motor function". European Journal of Biochemistry.
  6. (June 1999). "Size and charge requirements for kinetic modulation and actin binding by alkali 1-type myosin essential light chains". The Journal of Biological Chemistry.
  7. (August 1995). "A skeletal muscle-specific enhancer regulated by factors binding to E and CArG boxes is present in the promoter of the mouse myosin light-chain 1A gene". Molecular and Cellular Biology.
  8. (November 1986). "Cardiac myosin light and heavy chain isotypes in tetralogy of Fallot". Cardiovascular Research.
  9. (June 1986). "Myosin transitions in the bovine and human heart. A developmental and anatomical study of heavy and light chain subunits in the atrium and ventricle". Circulation Research.
  10. (December 2003). "Embryonic atrial function is essential for mouse embryogenesis, cardiac morphogenesis and angiogenesis". Development.
  11. (July 1996). "Regulation of human heart contractility by essential myosin light chain isoforms". The Journal of Clinical Investigation.
  12. (May 1997). "Different actin affinities of human cardiac essential myosin light chain isoforms". FEBS Letters.
  13. (July 2014). "Distinct interactions between actin and essential myosin light chain isoforms". Biochemical and Biophysical Research Communications.
  14. (August 2001). "Examining the in vivo role of the amino terminus of the essential myosin light chain". The Journal of Biological Chemistry.
  15. (June 1998). "Functional significance of cardiac myosin essential light chain isoform switching in transgenic mice". The Journal of Clinical Investigation.
  16. (April 2004). "Functional characterization of the human atrial essential myosin light chain (hALC-1) in a transgenic rat model". Journal of Molecular Medicine.
  17. (2005). "Sliding Filament Mechanism in Muscle Contraction". Springer.
  18. (May 1992). "Hemodynamic performance and myosin light chain-1 expression of the hypertrophied left ventricle in aortic valve disease before and after valve replacement". Circulation Research.
  19. (December 1984). "Myosin isoenzymes in human hypertrophic hearts. Shift in atrial myosin heavy chains and in ventricular myosin light chains". European Heart Journal.
  20. (February 1998). "Modulation of contractility in human cardiac hypertrophy by myosin essential light chain isoforms". Cardiovascular Research.
  21. (April 1997). "Changes in essential myosin light chain isoform expression provide a molecular basis for isometric force regulation in the failing human heart". Journal of Molecular and Cellular Cardiology.
  22. (September 1999). "Expression of atrial myosin light chains but not alpha-myosin heavy chains is correlated in vivo with increased ventricular function in patients with hypertrophic obstructive cardiomyopathy". Journal of Molecular Medicine.
  23. (2002). "A molecular mechanism improving the contractile state in human myocardial hypertrophy". Experimental and Clinical Cardiology.
  24. (November 2006). "Mutation of Arg723Gly in beta-myosin heavy chain gene in five Chinese families with hypertrophic cardiomyopathy". Chinese Medical Journal.
  25. (July 1993). "Three-dimensional structure of myosin subfragment-1: a molecular motor". Science.
  26. (June 2011). "Human essential myosin light chain isoforms revealed distinct myosin binding, sarcomeric sorting, and inotropic activity". Cardiovascular Research.

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