PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Myosin Light Chains”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1994

Secretion from rat basophilic RBL-2H3 cells is associated with diphosphorylation of myosin light chains by myosin light chain kinase as well as phosphorylation by protein kinase C.

The phosphorylation of myosin light chains and heavy chains by protein kinase C is known to be temporally correlated with Ca(2+)-dependent secretion of granules from RBL-2H3 cells (Ludowyke, R. I., Peleg, I., Beaven, M. A., and Adelstein, R. S. (1989) J. Biol. Chem. 264, 12492-12501). We now report that whereas myosin light chains are predominantly monophosphorylated by the Ca2+/calmodulin-dependent myosin light chain kinase at serine 19 in unstimulated cells, stimulation of RBL-2H3 cells with antigen or other stimulants causes additional phosphorylation of myosin light chains by myosin light chain kinase at threonine 18, as well as by protein kinase C at serine 1 or serine 2. This diphosphorylation at serine 19 and threonine 18 by myosin light chain kinase and the monophosphorylation by protein kinase C is correlated with the rate and extent of degranulation. Secretion occurs whenever phosphorylation by both enzymes is stimulated by antigen or by the combination of low concentrations of A23187 (50 nM) and phorbol 12-myristate 13-acetate (20 nM). These phosphorylations appear to be closely associated with exocytosis in RBL-2H3 cells. Thus, phosphorylation, as well as secretion, can be blocked by the kinase inhibitors KT5926 and ML-7. More specifically, phorbol ester alone induces phosphorylation of myosin light chains by protein kinase C exclusively, but fails to induce secretion until accompanied by low concentrations of A23187, which activates myosin light chain kinase. Conversely, selective suppression of phosphorylation by protein kinase C (with Ro31-7549 in antigen-stimulated cells) suppresses degranulation, thereby indicating a requirement for protein kinase C.

Alkaloids↗
PubMed1991

Effect of phosphorylation of myosin light chain by myosin light chain kinase and protein kinase C on conformational change and ATPase activities of human platelet myosin.

Human platelet myosin forms 10S and 6S conformations, and its Ca(2+)- and Mg(2+)-ATPase activities are parallel with the transition between 10S and 6S conformation, as judged by the gel filtration, intrinsic fluorescence, and viscosity methods. The 20,000-dalton myosin light chain (LC20) is phosphorylated by both myosin light chain kinase (MLC kinase) and Ca2+, phospholipid-dependent protein kinase (protein kinase C [PKC]). The phosphorylation (1 mol of phosphate/mol of LC20) by MLC kinase shifts the equilibrium toward the 6S conformation, but that by PKC does not. The prephosphorylation of myosin by PKC prevents the effect of phosphorylation by MLC kinase on actin-activated Mg(2+)-ATPase activity, but not the effect on conformational change. Inhibition of actin-activated ATPase activity by PKC is due to a decreased affinity of myosin for actin, and no change in Vmax is observed. These results suggest that sequential phosphorylation of myosin by both kinases plays an important role in the ATPase activities of human platelet myosin.

Actins↗
PubMed2003

Myosin light chain kinase stimulates smooth muscle myosin ATPase activity by binding to the myosin heads without phosphorylating the myosin light chain.

Myosin light chain kinase (MLCK) is a multifunctional regulatory protein of smooth muscle contraction [IUBMB Life 51 (2001) 337, for review]. The well-established mode for its regulation is to phosphorylate the 20 kDa myosin light chain (MLC 20) to activate myosin ATPase activity. MLCK exhibits myosin-binding activity in addition to this kinase activity. The myosin-binding activity also stimulates myosin ATPase activity without phosphorylating MLC 20 [Proc. Natl. Acad. Sci. USA 96 (1999) 6666]. We engineered an MLCK fragment containing the myosin-binding domain but devoid of a catalytic domain to explore how myosin is stimulated by this non-kinase pathway. The recombinant fragment thus obtained stimulated myosin ATPase activity by V(max)=5.53+/-0.63-fold with K(m)=4.22+/-0.58 microM (n=4). Similar stimulation figures were obtained by measuring the ATPase activity of HMM and S1. Binding of the fragment to both HMM and S1 was also verified, indicating that the fragment exerts stimulation through the myosin heads. Since S1 is in an active form regardless of the phosphorylated state of MLC 20, we conclude that the non-kinase stimulation is independent of the phosphorylating mode for activation of myosin.

Binding Sites↗
PubMed1987

Myosin light chain kinase and myosin light chain phosphatase from Dictyostelium: effects of reversible phosphorylation on myosin structure and function.

We have partially purified myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP) from Dictyostelium discoideum. MLCK was purified 4,700-fold with a yield of approximately 1 mg from 350 g of cells. The enzyme is very acidic as suggested by its tight binding to DEAE. Dictyostelium MLCK has an apparent native molecular mass on HPLC G3000SW of approximately 30,000 D. Mg2+ is required for enzyme activity. Ca2+ inhibits activity and this inhibition is not relieved by calmodulin. cAMP or cGMP have no effect on enzyme activity. Dictyostelium MLCK is very specific for the 18,000-D light chain of Dictyostelium myosin and does not phosphorylate the light chain of several other myosins tested. Myosin purified from log-phase amebas of Dictyostelium has approximately 0.3 mol Pi/mol 18,000-D light chain as assayed by glycerol-urea gel electrophoresis. Dictyostelium MLCK can phosphorylate this myosin to a stoichiometry approaching 1 mol Pi/mol 18,000-D light chain. MLCP, which was partially purified, selectively removes phosphate from the 18,000-D light chain but not from the heavy chain of Dictyostelium myosin. Phosphatase-treated Dictyostelium myosin has less than or equal to 0.01 mol Pi/mol 18,000-D light chain. Phosphatase-treated myosin could be rephosphorylated to greater than or equal to 0.96 mol Pi/mol 18,000-D light chain by incubation with MLCK and ATP. We found myosin thick filament assembly to be independent of the extent of 18,000-D light-chain phosphorylation when measured as a function of ionic strength. However, actin-activated Mg2+-ATPase activity of Dictyostelium myosin was found to be directly related to the extent of phosphorylation of the 18,000-D light chain. MLCK-treated myosin moved in an in vitro motility assay (Sheetz, M. P., and J. A. Spudich, 1983, Nature (Lond.), 305:31-35) at approximately 1.4 micron/s whereas phosphatase-treated myosin moved only slowly or not at all. The effects of phosphatase treatment on the movement were fully reversed by subsequent treatment with MLCK.

Alkaline Phosphatase↗
PubMed1997

Myocardial infarction and regulatory myosin light chain.

Myosin from cardiac muscle consists of two heavy chains and two pairs of light chain. Regulatory myosin light chain (RMLC) is phosphorylated by a Ca2+ and calmodulin dependent myosin light chain kinase. The impact of experimental myocardial infarction on cardiac RMLC was studied. The left anterior descending coronary artery of rabbits was ligated. Three, 7 and 14 days later the animals were euthanized, sections of the heart were frozen in liquid nitrogen and later subjected to 2-dimensional electrophoresis. Isoelectric focusing was carried out at a pH range of 4.5-5.4. Reproducible patterns of protein separation showed four spots with proteins of phosphorylatable regulatory light chains shifted to a more negative pH as compared to essential light chain. We investigated changes in phosphorylation of RMLC in infarcted heart muscle. As compared to sham operated animals, a decline in phosphorylation of RMLC was present in both infarcted and non-infarcted portions of the left ventricle; the latter was significant 7 days following the onset of ischemia. In contrast, the decline in percent phosphorylation in the infarcted area was not significant. The amount of RMLC decreased significantly in the infarcted portion. A highly significant reduction in the percent of viable cardiomyocytes accompanied the decline in phosphorylation. There was a significant correlation of RMLC following administration of isoproterenol, 7 and 14 days following onset of ischemia. Only faint traces of essential atrial myosin light chain (ALC-1) were present in the non-infarcted portion of the left ventricle. No correlation was found between percent phosphorylation and the amount of RMLC (density) following infusion of saline or isoproterenol. Isoproterenol significantly increased percent phosphorylation without altering the amount of RMLC protein. We conclude that myocardial infarction profoundly affects regulatory myosin light chain phosphorylation in the infarcted and non-infarcted areas of the myocardium and that RMLC plays a significant part in myocardial contractility.

Animals↗
PubMed1987

Effects of purified myosin light chain kinase on myosin light chain phosphorylation and catecholamine secretion in digitonin-permeabilized chromaffin cells.

Many non-muscle cells including chromaffin cells contain actin and myosin. The 20,000 dalton light chain subunits of myosin can be phosphorylated by a Ca2+/calmodulin-dependent enzyme, myosin light chain kinase. In tissues other than striated muscle, light chain phosphorylation is required for actin-induced myosin ATPase activity. The possibility that actin and myosin are involved in catecholamine secretion was investigated by determining whether increased phosphorylation in the presence of [gamma-32P]ATP of myosin light chain by myosin light chain kinase enhances secretion from digitonin-treated chromaffin cells. In the absence of exogenous myosin light chain kinase, 1 microM Ca2+ caused a 30-40% enhancement of the phosphorylation of a 20 kDa protein. This protein was identified on 2-dimensional gels as myosin light chain by its comigration with purified myosin light chain. Purified myosin light chain kinase (400 micrograms/ml) in the presence of calmodulin (10 microM) caused little or no enhancement of myosin light chain phosphorylation in the absence of Ca2+ in digitonin-treated cells. In the presence of 1 microM Ca2+, myosin light chain kinase (400 micrograms/ml) caused an approximately two-fold increase in myosin light chain phosphorylation in digitonin-treated cells in 5 min. The phosphorylation required permeabilization of the cells by digitonin and occurred within the cells rather than in the medium. Myosin light chain kinase-induced phosphorylation of myosin light chain was maximal at 1 microM Ca2+. Under identical conditions to those of the phosphorylation experiments, secretion was unaltered by myosin light chain kinase. The experiments indicate that the phosphorylation of myosin light chain by myosin light chain kinase is not a limiting factor in secretion in digitonin-treated chromaffin cells and suggest that the activation of myosin is not directly involved in secretion from the cells. The experiments also demonstrate the feasibility of investigation of effects of exogenously added proteins on secretion in digitonin-treated cells.

Adrenal Medulla↗
PubMed1982

The genes coding for the muscle contractile proteins, myosin heavy chain, myosin light chain 2, and skeletal muscle actin are located on three different mouse chromosomes.

The chromosomal distribution of murine genes expressed during differentiation of skeletal muscle cells was determined by Southern blot analysis of DNA from mouse-Chinese hamster hybrid cell lines containing incomplete subsets of mouse chromosomes. All detectable myosin heavy chain genes are located on chromosome 11. The gene for the myosin light chain 2 is located on chromosome 7. The skeletal muscle alpha-actin gene and several other actin genes, or pseudogenes, are located on chromosome 3. Additional actin DNA sequences are distributed on other mouse chromosomes.

Actins↗
PubMed2000

Regulation of LPA-promoted myofibroblast contraction: role of Rho, myosin light chain kinase, and myosin light chain phosphatase.

Myofibroblasts generate the contractile force responsible for wound healing and pathological tissue contracture. In this paper the stress-relaxed collagen lattice model was used to study lysophosphatidic acid (LPA)-promoted myofibroblast contraction and the role of the small GTPase Rho and its downstream targets Rho kinase and myosin light chain phosphatase (MLCPPase) in regulating myofibroblast contraction. In addition, the regulation of myofibroblast contraction was compared with that of smooth muscle cells. LPA-promoted myofibroblast contraction was inhibited by the myosin light chain kinase (MLCK) inhibitors KT5926 and ML-7; however, in contrast to that observed in smooth muscle cells, elevation of intracellular calcium alone was not sufficient to promote myofibroblast contraction. These results suggest that Ca(2+)-mediated activation of MLCK, while necessary, is not sufficient to promote myofibroblast contraction. The specific Rho inactivator C3-transferase and the Rho kinase inhibitor Y-27632 inhibited LPA-promoted myofibroblast contraction, suggesting that contraction depends on activation of the Rho/Rho kinase pathway. Calyculin, a type 1 phosphatase inhibitor known to inhibit MLCPPase, could promote myofibroblast contraction in the absence of LPA, as well as restore contraction in the presence of C3-transferase or Y-27632. Together these results support a model whereby Rho/Rho kinase-mediated inhibition of MLCPPase is necessary for LPA-promoted myofibroblast contraction, in contrast to smooth muscle cells in which Ca(2+) activation of MLCK alone is sufficient to promote contraction.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1997

Analysis of cDNAs encoding Drosophila melanogaster myosin light chain kinase.

Myosin light chain kinase regulates the activity of myosin by phosphorylating the myosin regulatory light chain. Here we describe the cloning and characterization of cDNAs encoding Drosophila melanogaster myosin light chain kinase. We amplified a fragment of the Drosophila mlck gene using degenerate primers homologous to a highly conserved region in myosin light chain kinase proteins of vertebrate species. We used the gene fragment to isolate corresponding Drosophila mlck cDNAs. The deduced protein sequence of the cDNAs shows high homology to the catalytic and regulatory domains of vertebrate nonmuscle, smooth muscle and skeletal muscle myosin light chain kinase. Protein motifs I and II, which are present in vertebrate nonmuscle and smooth muscle myosin light chain kinase, but not in skeletal muscle myosin light chain kinase, are also present in Drosophila myosin light chain kinase. Transcript and cDNA analysis shows the gene encodes multiple messages and is expressed in nonmuscle and muscle cells, including the adult indirect flight muscle. Genomic Southern analysis and chromosome hybridization suggest mlck is a single copy gene which maps to chromosome band 52D, and is not haplo-insufficient for flight.

Amino Acid Sequence↗
PubMed2000

Myosin light chain kinase transference induces myosin light chain activation and endothelial hyperpermeability.

The actomyosin complex is the major cytoskeletal component that controls cell contraction. In this study, we investigated the effects of actomyosin interaction on endothelial barrier function and gap formation. Activated myosin light chain kinase (MLCK) protein was transferred into coronary venular endothelial cell (CVEC) monolayers. Uptake of the activated protein resulted in a significant shift in myosin light chain (MLC) from an unphosphorylated to a diphosphorylated form. In addition, MLCK induced a hyperpermeability response of the monolayer as measured by albumin transendothelial flux. Microscopic examination of MLCK-treated CVECs revealed widespread gap formation in the monolayer, loss of peripheral beta-catenin, and increases in actin stress fibers. Inhibition of all of the above responses by a specific MLCK inhibitor suggests they are the direct result of exogenously added MLCK. These data suggest that activation of MLCK in CVECs causes phosphorylation of MLC and contraction of CVECs, resulting in gap formation and concomitant increases in permeability. This study uses a novel technique to measure the effects of an activated kinase on both its substrate and cellular morphology and function through direct transference into endothelial cells.

Actins↗
PubMed1983

Separation and identification of Drosophila myosin light chains.

Myosin was extracted from the larvae and adult flies of Drosophila melanogaster, and purified by column chromatography in the presence of KI. Myosin light chains were separated from heavy chains by column chromatography after treatment of the myosin with urea, and they were identified by 2D-gel electrophoresis. Tubular muscles and fibrillar muscles have different light chains. Lt1 (Mw = 31,000), Lt2 (Mw = 30,000), Lt2' (Mw = 30,000), and Lt3 (Mw = 20,000) exist in the tubular myosin of both larvae and adult flies; Lf1 (Mw = 34,000), Lf2 (Mw = 30,000), Lf2' (Mw = 30,000), and Lf3 (Mw = 20,000) exist in the fibrillar myosin. Polyacrylamide gel electrophoresis of myosin under nondissociating conditions revealed that there was one major myosin isozyme in each type of adult muscle, and the re-electrophoresis of each isozyme on SDS gel confirmed our identification of the light chains.

Animals↗
PubMed1983

Effects of relaxin on rat uterine myosin light chain kinase activity and myosin light chain phosphorylation.

Isometrically suspended uteri from estrogen-primed rats were stimulated with prostaglandin F2 alpha and then exposed to relaxin. Relaxin-dependent decreases in the ratio of phosphorylated to total myosin light chains (MLC) and in MLC kinase activity, measured in the presence of 0.5 mg/ml of uterine myosin and the absence and presence of Ca2+-calmodulin (CaM), were observed. The time-course and concentration-response of these biochemical effects of relaxin paralleled the hormone-induced inhibition of uterine contractile activity. Relaxin treatment resulted in a change in the requirements of MLC kinase for Ca2+, CaM, and myosin. Titrations of MLC kinase activity showed a shift in K50 values for Ca2+ from 82 to 260 nM and for CaM from 2.2 to 25 nM in extracts from control and relaxin-treated tissues, respectively. The myosin Km values of MLC kinase from control and relaxin-treated tissues were 0.33 and 0.71 mg/ml, respectively. Under optimal assay conditions (100 microM Ca2+, 1 microM CaM, and 1.2 mg/ml of myosin) the activities of MLC kinase in both extracts were identical, regardless of hormone concentration or exposure time. These data suggest that relaxin-treatment results in a change in the affinity of MLC kinase for its substrate and modulator and that relaxin inhibits uterine contractile activity by a mechanism which involves a decrease in MLC kinase activity and, in turn, a decrease in phosphorylation of the 20,000-dalton light chains of myosin.

Animals↗
PubMed2006

Microfilament-binding properties of N-terminal extension of the isoform of smooth muscle long myosin light chain kinase.

Myosin light chain kinases (MLCK) phosphorylate the regulatory light chain of myosin II in thick filaments and bind to F-actin-containing thin filaments with high affinity. The ability of short myosin light chain kinase (S-MLCK) to bind F-actin is structurally attributed to the DFRXXL regions in its N-terminus. The long myosin light chain kinase (L-MLCK) has two additional DFRXXL motifs and six Ig-like modules in its N-terminal extension. The six Ig-like modules are capable of binding to stress fibers independently. Our results from the imaging analysis demonstrated that the first two intact Ig-like modules (2Ig) in N-terminal extension of L-MLCK is the minimal binding module required for microfilament binding. Binding assay confirmed that F-actin was able to bind 2Ig. Stoichiometries of 2Ig peptide were similar for myofilament or pure F-actin. The binding affinities were slightly lower than 5DFRXXL peptide as reported previously. Similar to DFRXXL peptides, the 2Ig peptide also caused efficient F-actin bundle formation in vitro. In the living cell, over-expression of 2Ig fragment increased "spike"-like protrusion formation with over-bundled F-actin. Our results suggest that L-MLCK may act as a potent F-actin bundling protein via its DFRXXL region and the 2Ig region, implying that L-MLCK plays a role in cytoskeleton organization.

Actins↗
PubMed1991

Purification and characterization of pregnant sheep myometrium myosin light chain kinase.

Myosin light chain kinase (MLCK) has been purified from the myometrium of pregnant sheep. The Mr of the enzyme was determined from SDS-polyacrylamide gels to be 160,000. It requires Ca2+ and calmodulin for activation, and phosphorylates the 20,000-Da light chains of myosin at a rapid rate. The specific activity for the myosin light chains from turkey gizzards and rabbit uterine muscle are 7.7 and 5.4 mumol/min/mg, respectively. The Km for the former substrate is 40 microM and the Vmax of the reaction is 19 mumol/min/mg. Polyclonal antibodies raised against the enzyme cross-reacted with pregnant sheep myometrium (psm), turkey gizzard (tg), and chicken gizzard MLCK. Affinity purification of the antibodies on tg-MLCK Sepharose resulted in the preparation of two fractions of antibodies with different reactivity toward these proteins. Fraction A antibodies which did not bind to the affinity column cross-reacted only with psm-MLCK while Fraction B antibodies which bound to the column cross-reacted with all three proteins. Western blots of extracts of turkey gizzards, human myometrium, and various tissues from sheep showed cross-reactivity of both fractions of antibodies with a 160,000-Da protein in the extracts of sheep smooth muscles. Only Fraction B antibodies cross-reacted with a protein (130,000 Da) in turkey gizzards and human myometrium extracts. Prolonged tryptic digestion of psm-MLCK produced large fragments Mr approximately 60,000 which appears to be similar to that formed from tg-MLCK, and some smaller peptides. Fraction A antibodies cross-reacted with the small peptides while Fraction B antibodies cross-reacted with the large fragments but not vice versa. Further analysis of the tryptic peptides suggests that the epitopes of Fraction A antibodies are localized in a peptide which appears to be in the NH2-terminal region of the molecule.

Animals↗
PubMed1988

Coexpression and assembly of myosin heavy chain and myosin light chain in Escherichia coli.

A fragment of the Dictyostelium discoideum myosin heavy chain gene representing heavy meromyosin was coexpressed in Escherichia coli with the entire essential myosin light chain from the scallop. The expressed myosin heavy chain and essential myosin light chain copurify through ammonium sulfate fractionation, anion exchange, and gel filtration chromatography. The purified complex consists of about 1 mol of light chain per mol of heavy chain. This stoichiometry, which is that of native myosin, suggests that no special eukaryotic machinery is required for coassembly of these two proteins. By coexpressing different myosin heavy chain and myosin light chain combinations, it should be possible to study various isoforms of these two proteins, which are both products of multigene families in mammals. E. coli is thus an ideal system in which to study expression and multimeric assembly of individual components of the eukaryotic contractile apparatus.

Amino Acid Sequence↗
PubMed2003

The characterization of Ca(2+)-calmodulin independent phosphorylation of myosin light chains by a fragment from myosin light chain kinase.

A constitutively active myosin light chain kinase (MLCK) fragment (MLCKF) was found to phosphorylate myosin light chains (MLC(20)) in a Ca(2+)-CaM independent way more effectively than the intact MLCK. The MLCKF was prepared by tryptic digestion of MLCK. Western blot was used to demonstrate the homogeneity of trypsin-digested MLCKF and intact MLCK. Phosphorylation of MLC(20) was detected by Gly-PAGE and Scoin Image Software, and Mg(2+)-ATPase activity of myosin was measured with spectrophotometry. Our results indicated that Ca(2+)-CaM independent phosphorylation of myosin (CIPM) by MLCKF was more efficient than CIPM by MLCK and less efficient than Ca(2+)-CaM dependent phosphorylation of myosin (CDPM) by MLCK in phosphorylating MLC(20) and stimulating myosin Mg(2+)-ATPase activity; both CIPM by MLCKF and CIPM by MLCK were less influenced by the rise of incubation-temperature, the prolonging of incubation-time, the increase of ionic strength of KCl and less sensitive to MLCK inhibitor ML-9 1-(5-chloronaphthalene-1-sulfonyl) -1H-hexahydro-1,4-diazepine than CDPM by MLCK. The differences were statistically significant ((P)<0.01, or (P)<0.05). The results may be valuable to further investigating the mechanisms of sustained tension characterized by less energy consumption.

Blotting, Western↗
PubMed1985

The influence of P-light chain phosphorylation by myosin light chain kinase on the calcium sensitivity of chemically skinned heart fibres.

Phosphorylation of the P-light chain of myosin might be involved in the regulation of cardiac contractility. Thus an enhanced phosphorylation level of the P-light chain catalyzed by Ca2+-calmodulin-dependent myosin light chain kinase (MLCK) increased significantly the Ca2+ sensitivity of chemically skinned ventricular fibre bundles of the pig. This effect was reversible. Whereas force development at submaximal Ca2+ concentration (pCa 5.5) increased by approximately 50% in the presence of MLCK, maximum tension achieved at maximum Ca2+-concentration (pCa 4.3) was not affected.

Animals↗