Myosin Light Chain

Non muscle Myosins are required for cytokinesis at the end of cell division, when a contractile ring near the plasmalemma divides the cytoplasm of the daughter cells. They are involved in cytoplasmic streaming movements in tissues, and especially in activation of motile cells such as fibroblasts and macrophages. Activation of non-muscle myosin-II is achieved by phosphorylation of Ser33 in the motif KKRPQRATSN by a dedicated, Ca +2 Calmodulin regulated light chain kinase (MLCK).

Myosin regulatory light chains, including MRCL3, MYLPF and MYL9, regulate contraction in smooth muscle and non-muscle cells via phosphorylation by MLCK (myosin light chain kinase). Phosphorylation of myosin regulatory light chains, catalyzed by MLCK in the presence of calcium and calmodulin, increases the actin-activated myosin ATPase activity, thus regulating the contractile activity. MYLPF is vital for fast and slow skeletal muscle development.

MYL9 is one of the numerous regulatory myosin light chains. Myosin which is a structural component of the muscle consists of 2 heavy chains and 4 light chains. MYL9 is a myosin light chain regulates muscle contraction by modulating the ATPase activity of myosin heads. MYL9 binds calcium and is activated by myosin light chain kinase. Regulatory myosin light chains regulate contraction in smooth muscle and non-muscle cells via phosphorylation by MLCK (myosin light chain kinase). Phosphorylation of regulatory myosin light chains is catalyzed by MLCK in the presence of calcium and calmodulin and it increases the actin-activated myosin ATPase activity, thus regulates the contractile activity.

MYL9 is one of the numerous regulatory myosin light chains. Myosin which is a structural component of the muscle consists of 2 heavy chains and 4 light chains. MYL9 is a myosin light chain regulates muscle contraction by modulating the ATPase activity of myosin heads. MYL9 binds calcium and is activated by myosin light chain kinase. Regulatory myosin light chains regulate contraction in smooth muscle and non-muscle cells via phosphorylation by MLCK (myosin light chain kinase). Phosphorylation of regulatory myosin light chains is catalyzed by MLCK in the presence of calcium and calmodulin and it increases the actin-activated myosin ATPase activity, thus regulates the contractile activity.

MYL7 protein is an atrial isoform of myosin regulatory light chain 2 (MYL2). Myosin is a hexamer containing 4 light chains and 2 heavy chains. MYL7 is mainly expressed in adult atrial muscle.

Myosin Light Chain 6B (MYL6B) is a heavy chain regulator located in smooth muscle and non-muscle Myosin complexes. Contractile activity in the smooth muscle is regulated by the calcium/calmodulin-dependent phosphorylation of Myosin light chain by Myosin light chain kinase. MYL6B doesn’t bind calcium during contraction. MYL6B is mostly found as a hexamer consisting of 4 light chains and 2 heavy chains. MYL6B usually interacts with Myosin Va, an Actin based motor which moves in large steps. MYL6B is expressed in the majority of tissues with neurons, while smooth muscle tissue having the highest expression.

Myosin light polypeptide 6 (MYL6) is a hexameric ATPase cellular motor protein. MYL6 is composed of 2 heavy chains, 2 nonphosphorylatable alkali light chains, and 2o phosphorylatable regulatory light chains. MYL6 is a myosin alkali light chain which is expressed in smooth muscle and non-muscle tissues. MYL6 partakes in generating the force for cellular movements, thus having an imperative role in overall cellular function.

Myosin regulatory light chain 5 (MYL5) is a hexameric ATPase cellular motor protein. Myosin is comprised of 2 heavy chains, 2 nonphosphorylatable alkali light chains, and 2 phosphorylatable regulatory light chains. MYL5 is a regulatory light chain and is expressed in the fetal muscle and in the adult retina, cerebellum, and basal ganglia. The reconstitution of myosin with MYL5 or alkali light chain increases filament velocity to intermediate rates, and the re-addition of both classes of light chains fully reinstates the original sliding pace.

Myosin regulatory light chain 5 (MYL5) is a hexameric ATPase cellular motor protein. Myosin is comprised of 2 heavy chains, 2 nonphosphorylatable alkali light chains, and 2 phosphorylatable regulatory light chains. MYL5 is a regulatory light chain and is expressed in the fetal muscle and in the adult retina, cerebellum, and basal ganglia. The reconstitution of myosin with MYL5 or alkali light chain increases filament velocity to intermediate rates, and the re-addition of both classes of light chains fully reinstates the original sliding pace.

MYL4 is a hexameric ATPase cellular motor protein which is composed of two nonphosphorylatable alkali light chains, two heavy chains and two phosphorylatable regulatory light chains. MYL4 encodes a myosin alkali light chain which is located in embryonic muscle and adult atria. Two alternatively spliced transcript variants encoding the same protein were found for this gene.

MYL2 regulatory light chain is associated with cardiac myosin beta (or slow) heavy chain. Ca+ activates the phosphorylation of regulatory light chain that in turn activates contraction. Mutations in this MYL2 gene are related with mid-left ventricular chamber type hypertrophic cardiomyopathy. MYL2 is an essential protein that plays a role in the regulation of myosin ATPase activity in smooth muscle. MYL2 phosphorylation is regulated by ROCK and MLC kinase and is involved in platelet biogenesis by controlling proplatelet formation and fragmentation.

Myosin is composed of 2 nonphosphorylatable alkali light chains, 2 heavy chains and 2 phosphorylatable regulatory light chains. MYL12B is a hexameric ATPase cellular motor protein which controls contraction in smooth muscle and non-muscle cells through phosphorylation by myosin light chain kinase (MLCK). Phosphorylation of myosin regulatory light chains catalyzed by MLCK in the presence of calcium and calmodulin, rises Actin-activated myosin ATPase activity, thus regulating contractile activity.

Myosin regulatory light chain 12A (MYL12A) has a vital role in regulation of both smooth muscle and nonmuscle cell contractile activity via its phosphorylation. The MYL12A protein is involved in cytokinesis, receptor capping, and cell locomotion.

Myosin is a hexameric ATPase cellular motor protein, which is composed of 2 heavy chains, 2 non-phosphorylatable alkali light chains, and 2 phosphorylatable regulatory light chains.
MYL1 gene encodes a myosin alkali light chain expressed in fast skeletal muscle. Two transcript variants have been identified for the MYL1 gene. In humans MYL1 is localized to chromosome 2q32.1-qter. The Myl1 locus encodes two alkali myosin light chains- Mlc1f and Mlc3f, from two promoters that are differentially regulated throughout development. The Mlc1f promoter is active in embryonic, fetal and adult fast skeletal muscle while the Mlc3f promoter is upregulated during fetal development and stays on in adult fast skeletal muscle.

Myosin Binding Protein C, Cardiac (MYBPC3) is the cardiac isoform of myosin-binding protein C expressed exclusively in heart muscle. Myosin-binding protein C is a myosin-associated protein found in the cross-bridge-bearing zone (C region) of A bands in striated muscle. Regulatory phosphorylation of the cardiac isoform in vivo by cAMP-dependent protein kinase upon adrenergic stimulation may be associated with modulation of cardiac contraction. MYBPC3 gene mutations are one of the causes of familial hypertrophic cardiomyopathy. In vitro MYBPC3 binds MHC, F-actin and native thin filaments, and modifies the activity of actin-activated myosin ATPase. MYBPC3 may modulate muscle contraction or it may have a more structural role.