Myosin essential light chain (ELC), ventricular/cardiac isoform is a protein that in humans is encoded by the MYL3gene.[5][6][7] This cardiac ventricular/slow skeletal ELC isoform is distinct from that expressed in fast skeletal muscle (MYL1) and cardiac atrial muscle (MYL4). Ventricular ELC is part of the myosin molecule and is important in modulating cardiac muscle contraction.
Cardiac, ventricular ELC is 21.9 kDa and composed of 195 amino acids (See human MYL3 sequences features hereArchived 2015-09-24 at the Wayback Machine). Cardiac ELC and the second light chain, regulatory light chain (RLC, MYL2), are non-covalently bound to IQXXXRGXXXR motifs in the 9 nm S1-S2 lever arm of the myosin head,[8] both alpha (MYH6) and beta (MYH7) isoforms. Both light chains are members of the EF-hand superfamily of proteins, which possess helix-loop-helix motifs in two globular domains connected by an alpha-helical linker. Though EF hand motifs are specialized to bind divalent ions such as calcium, cardiac ELC does not bind calcium at physiological levels.[9] The N-terminal region of cardiac ELC is functionally unique in that it is positively charged, being rich in Lysine residues (amino acids 4-14), with subsequent unique structure governed by proline-alanine repeats (amino acids 15-36).
Studies have provided evidence for ELC as modulator of myosin crossbridge kinetics. Treating cardiac myofibrils with the lysine-rich N-terminal peptide (amino acids 5-14) evoked a supramaximal increase in cardiac myofibrillar MgATPase activity at submaximal calcium concentrations,[10] and further studies demonstrated that this region of ELC modulates the affinity of myosin for actin.[11]
Mutations in MYL3 have been identified as a cause of familial hypertrophic cardiomyopathy, and associated with a mid-left ventricular chamber type hypertrophy.[12] Five mutations in MYL3 have been identified to date: M149V, R154H, E56G, A57G and E143K.[13][14][15][16] All of these cluster around two of the four EF-hand domains, suggesting that proper conformation in these regions is necessary for normal cardiac function.[12]
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^Shi Q, Li RK, Mickle DA, Jackowski G (November 1992). "Analysis of the upstream regulatory region of human ventricular myosin light chain 1 gene". Journal of Molecular and Cellular Cardiology. 24 (11): 1221–9. doi:10.1016/0022-2828(92)93089-3. PMID1479618.
^Cohen-Haguenauer O, Barton PJ, Van Cong N, Cohen A, Masset M, Buckingham M, Frézal J (February 1989). "Chromosomal assignment of two myosin alkali light-chain genes encoding the ventricular/slow skeletal muscle isoform and the atrial/fetal muscle isoform (MYL3, MYL4)". Human Genetics. 81 (3): 278–82. doi:10.1007/bf00279004. PMID2784124. S2CID6703175.
^Stepkowski D, Efimova N, Paczyņska A, Moczarska A, Nieznańska H, Kakol I (June 1997). "The possible role of myosin A1 light chain in the weakening of actin-myosin interaction". Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology. 1340 (1): 105–14. doi:10.1016/s0167-4838(97)00031-9. PMID9217020.
^Poetter K, Jiang H, Hassanzadeh S, Master SR, Chang A, Dalakas MC, Rayment I, Sellers JR, Fananapazir L, Epstein ND (May 1996). "Mutations in either the essential or regulatory light chains of myosin are associated with a rare myopathy in human heart and skeletal muscle". Nature Genetics. 13 (1): 63–9. doi:10.1038/ng0596-63. PMID8673105. S2CID742106.
^Lee W, Hwang TH, Kimura A, Park SW, Satoh M, Nishi H, Harada H, Toyama J, Park JE (February 2001). "Different expressivity of a ventricular essential myosin light chain gene Ala57Gly mutation in familial hypertrophic cardiomyopathy". American Heart Journal. 141 (2): 184–9. doi:10.1067/mhj.2001.112487. PMID11174330. S2CID23534623.
Henry GD, Trayer IP, Brewer S, Levine BA (April 1985). "The widespread distribution of alpha-N-trimethylalanine as the N-terminal amino acid of light chains from vertebrate striated muscle myosins". European Journal of Biochemistry. 148 (1): 75–82. doi:10.1111/j.1432-1033.1985.tb08809.x. PMID3979397.
Kovalyov LI, Shishkin SS, Efimochkin AS, Kovalyova MA, Ershova ES, Egorov TA, Musalyamov AK (July 1995). "The major protein expression profile and two-dimensional protein database of human heart". Electrophoresis. 16 (7): 1160–9. doi:10.1002/elps.11501601192. PMID7498159. S2CID32209361.
Poetter K, Jiang H, Hassanzadeh S, Master SR, Chang A, Dalakas MC, Rayment I, Sellers JR, Fananapazir L, Epstein ND (May 1996). "Mutations in either the essential or regulatory light chains of myosin are associated with a rare myopathy in human heart and skeletal muscle". Nature Genetics. 13 (1): 63–9. doi:10.1038/ng0596-63. PMID8673105. S2CID742106.
Takeuchi K, Senba S, Furukawa K, Eto M, Morita F (February 1999). "Localization of 17-kDa myosin light chain isoforms in cultured aortic smooth muscle cells". Journal of Biochemistry. 125 (2): 334–42. doi:10.1093/oxfordjournals.jbchem.a022291. PMID9990131.
