Myosin essential light chain (ELC), ventricular/cardiac isoform is a protein that in humans is encoded by the MYL3 gene.^[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.

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MYL3
Identifiers
Aliases	MYL3, CMH8, MLC1SB, MLC1V, VLC1, MLC-lV/sb, VLCl, myosin light chain 3
External IDs	OMIM: 160790; MGI: 97268; HomoloGene: 20099; GeneCards: MYL3; OMA:MYL3 - orthologs
Gene location (Human) Chr. Chromosome 3 (human)[1] Band 3p21.31 Start 46,835,111 bp[1] End 46,882,172 bp[1]
Gene location (Mouse) Chr. Chromosome 9 (mouse)[2] Band 9 F2|9 60.69 cM Start 110,570,929 bp[2] End 110,598,866 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in right ventricle triceps brachii muscle thoracic diaphragm vastus lateralis muscle gastrocnemius muscle tibialis anterior muscle body of tongue deltoid muscle vena cava kidney Top expressed in interventricular septum myocardium of ventricle cardiac muscles atrioventricular valve soleus muscle endocardial cushion right ventricle plantaris muscle esophagus aortic valve More reference expression data BioGPS More reference expression data
Gene ontology Molecular function calcium ion binding structural constituent of muscle cytoskeletal motor activity actin monomer binding myosin II heavy chain binding Cellular component cytosol muscle myosin complex sarcomere A band I band myosin complex Biological process ventricular cardiac muscle tissue morphogenesis regulation of striated muscle contraction skeletal muscle tissue development positive regulation of ATP-dependent activity cardiac muscle contraction regulation of the force of heart contraction muscle filament sliding Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 4634 17897 Ensembl ENSG00000160808 ENSMUSG00000059741 UniProt P08590 P09542 RefSeq (mRNA) NM_000258 NM_010859 NM_001364484 RefSeq (protein) NP_000249 NP_000249.1 NP_034989 NP_001351413 Location (UCSC) Chr 3: 46.84 – 46.88 Mb Chr 9: 110.57 – 110.6 Mb PubMed search [3] [4]
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Cardiac, ventricular ELC is 21.9 kDa and composed of 195 amino acids (See human MYL3 sequences features here Archived 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]