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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We find that extraction of as little as one troponin C molecule per troponin-tropomyosin strand on a thin filament reduces the slope of the pCa/tension relation. We interpret this to mean that the regulatory units along a thin filament of rabbit psoas fibers are linked co-operatively so that a thin filament activates as a unit. The presence of extended co-operativity explains why the pCa/tension relation in skinned fibers has a slope much higher than predicted by binding of Ca2+ to one regulatory unit. Replacement of the extracted troponin C with purified troponin C fully reverses the effect of extraction and shows it to be the essential Ca2+ binding protein responsible for the steep slope of the pCa/tension relation.
J Mol Biol 1984 Dec 05
PMID:The thin filament of vertebrate skeletal muscle co-operatively activates as a unit. 654 94

Purkinje cells from false tendons of young rabbits, pigs and fetal lambs were dispersed by the action of collagenase and elastase and grown in culture for up to 14 days. Immunofluorescent staining with fluorescein-labelled antibodies to cardiac myosin and tropomyosin demonstrated cross-banding and/or a diffuse positive stain in Purkinje cells between 3 and 7 days in culture. Electron microscopy of cultured Purkinje cells at 3 days and 7 days revealed some disorganization of the myofilament system, in particular loss of Z-band material, as well as many thickened Z-bands, 120 nm to 240 nm in width. Gap junctions remained but desmosomes and fasciae adherentes were fewer in number. Organelles such as ribosomes, glycogen and mitochondria did not alter. Some Purkinje cells were spontaneously contractile in culture for up to seven days. Dominguez and Fozzard [7] propose that buckling of the Purkinje fibre and the production of sarcolemmal folds on the cell surface affect conduction of electrical impulses. We suggest that Purkinje cell contraction may play a major part in producing these geometric changes affecting conduction.
J Mol Cell Cardiol 1983 Mar
PMID:Cardiac Purkinje cells in culture. 668 23

A charge variant of a protein (Tm: 3; molecular weight approximately 35,000) that co-migrates with human smooth muscle tropomyosin has been found in whole cell extracts from the fibroblasts of a father and his son. The variant protein co-purifies with Tm: 3, shifts with it to a higher apparent molecular weight on sodium dodecyl sulfate/polyacrylamide gel electrophoresis in the presence of 4 M-urea, is a component of the microfilaments, and has a peptide cleavage pattern identical to that of Tm: 3 and smooth muscle tropomyosin. The results indicate that Tm: 3 and the variant (Tm: 3.1) are smooth muscle tropomyosin, suggesting that normal human fibroblasts synthesize at least two tropomyosins (Tm:3 and the non-muscle tropomyosin Tm:4, molecular weight approximately 30,000) and that they are the products of separate genes.
J Mol Biol 1984 Feb 15
PMID:An electrophoretic variant of a human fibroblast protein with characteristics of smooth muscle tropomyosin. 669 12

In the presence of spermine tropomyosin forms sheets having two-dimensional crystallinity and tactoids. The most common form of sheet has cmm symmetry with a = 80 nm and b = 5 nm. The structure of this sheet has been solved in projection to a nominal resolution of 1.5 nm by combining data from electron diffraction and electron microscopy. Analysis of this pattern and that of rarely observed sheets having p2 symmetry (a = 40 nm, b = 5 nm and gamma = 80 degrees) indicated that the cmm structure was formed by superposition of two p2 sheets. The tropomyosin molecules in each p2 sheet were arranged in rows directed along the p2 (0,1) lattice lines, with all the molecules in one row having the same polarity and lying antiparallel to the molecules in adjacent rows. These rows associated in pairs, possibly by the supercoiling of the molecules in one row about those in the neighbouring row.
J Mol Biol 1984 Mar 25
PMID:Crystalline sheets of tropomyosin. 671 79

The cytoskeletal extracts of cultured human fibroblasts were found to contain at least four distinct polypeptides, each of which demonstrated the resistance to denaturation and the acidic isoelectric point characteristic of tropomyosin. One of these, hscp 36 (heat-stable cytoskeletal protein having an apparent molecular weight of 36,000), cross-reacted efficiently with an antiserum to chicken skeletal muscle tropomyosin. Furthermore, the messenger RNA coding for hscp 36 was selected by a chicken complementary DNA clone containing a tropomyosin sequence. The abundance of mRNA coding for hscp 36 was found to be similar in both normal and simian virus 40 (SV40) transformed human fibroblasts. The apparent molecular weight of hscp 36 is different from non-muscle tropomyosins previously isolated from human sources, which show the apparent molecular weight of 30,000 normally associated with non-muscle tropomyosin. This, together with the complexity of the heat-stable cytoskeletal proteins present in human fibroblasts, suggests the existence of multiple genes coding for human non-muscle tropomyosins.
J Mol Biol 1983 Feb 15
PMID:Novel form of non-muscle tropomyosin in human fibroblasts. 684 92

The fluorescence properties of rabbit cardiac tropomyosin specifically labeled at Cys190 with didansylcystine has been correlated with its unfolding transitions. Circular dichroism studies at 222 nm showed that for both didansylcystine-labeled tropomyosin and reduced tropomyosin under physiological conditions, a small thermal pretransition near 30 degrees C was present before the main unfolding transition at 48 degrees C. In the absence of added salt there was only one unfolding transition near 33 degrees C for both the native and the labeled tropomyosin. Thus, conformational perturbation by the probe was minor. Despite the specific labeling, the fluorescence decay of didansylcystine-labeled tropomyosin was composed of two components; a major component with a short lifetime (6 ns) and a minor blue shifted component with a relatively long lifetime (17 ns), due to the sampling by the probe of both a polar and a hydrophobic environment, respectively, near Cys190. The fluorescence contribution of the long-lived component increased in the pretransition before decreasing in the main unfolding transition. The increase of the long-lived component appears to be a consequence of a shift in conformational equilibrium of tropomyosin from a "chain-closed" toward a localized "chain-open" state, which allows greater access of the probe to the exposed hydrophobic region.
J Mol Biol 1983 Jun 25
PMID:Two conformational states of didansylcystine-labeled rabbit cardiac tropomyosin. 686 6

A myofibrillar protein extract has been isolated from the muscle of Ascaris suum. Two-dimensional electrophoresis of this extract revealed that the myosin light chain 1 (ALC1) migrates as 3 components with approximate isoelectric points in the range of 5.3-5.6. The most acidic component of ALC1 appeared to be phosphorylated when the myofibrillar extract was incubated for 10 s with catalytic subunit of cAMP dependent protein kinase and [gamma-32P] ATP. The myosin light chain 2 (ALC2) migrated as a single component in isoelectric focusing with an approximate isoelectric point of 5.5 Actin was resolved into 2 components with identical molecular weight but isoelectric points differing by approximatley 0.2 pH units. A protein was tentatively identified in the myofibrillar extract as tropomyosin. It migrated as a single band with an approximate isoelectric point of 5.0 and a molecular weight of 39 000. None of the troponin components could be identified in the myofibrillar extract. It is postulated that muscle contraction in A. suum muscle could be controlled by phosphorylation of myosin.
Mol Biochem Parasitol 1981 Jun
PMID:Electrophoretic analyses of myofibrillar proteins from the body wall muscles of Ascaris suum. 689 80

The binding of myosin subfragment-1 (S-1) to the F-actin-troponin-tropomyosin complex (regulated F-actin) was examined in the presence of ADP (ionic strength, 0.23 M; 22 degrees C) by using the ultracentrifuge and S-1 blocked at SH1 with iodo[14C]acetamide. S-1 . ADP binds with positive cooperativity to regulated F-actin, both in the presence and absence of calcium; it binds independently to unregulated actin. With and without Ca2+ at very low levels of occupancy of the regulated actin by S-1 . ADP, S-1 . ADP binds to the regulated actin with less than 1% of the strength that it binds to unregulated actin, whereas at high levels of occupancy of the regulated actin by S-1 . ADP, S-1 . ADP binds about 3-fold more strongly to the regulated actin than it does to unregulated actin. The major difference between the results obtained in the presence and absence of Ca2+ with regulated actin is that, in the absence of Ca2+, the binding of S-1 . ADP remains weak until a higher free S-1 . ADP concentration is reached and the transition to strong binding is much more cooperative. These results are consistent with a model that is basically similar to the cooperative binding model of Hill[Hill, T.L. (1952) J. Chem. Phys. 20, 1259-1273] and of Monod et al. [Monod, J., Wyman, J. & Changeux, J. (1965) J. Mol. Biol. 12, 88-118]: The regulated actin filament can exist in two forms, a weak-binding and a strong-binding form; and Ca2+ and S-1 . ADP, acting as allosteric effectors, shift the equilibrium between the two forms.
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PMID:Cooperative binding of myosin subfragment-1 to the actin-troponin-tropomyosin complex. 693 Jun 56

The binding of rabbit skeletal muscle troponin-T and several of its fragments to various types of tropomyosin immobilized on Sepharose 4B affinity columns equilibrated with 0.1 M NaCl, pH 7.0 buffer has been investigated. With rabbit skeletal muscle alpha-tropomyosin, intact troponin-T was eluted with an NaCl gradient at 0.42 M, while its fragments T1 (residues 1-158) and CB1 (residues 1-151) were eluted at 0.32 M NaCl in either "plus" or "minus" Ca2+ buffer in the presence of troponin-C. Fragment T2 (residues 159-259) was eluted at 0.22 M NaCl in minus Ca2+ buffer in the presence of troponin-C, but in the void volume with troponin-C under plus Ca2+ conditions. With immobilized nonpolymerizable alpha-tropomyosin, T1 was not bound, whereas T2 was eluted at the same NaCl concentration (0.21 M) as with alpha-tropomyosin. This binding was sensitive to Ca2+ in the presence of troponin-C. The results are consistent with a structural interpretation of a two-site model of troponin attachment to alpha-tropomyosin (Mak, A. S., and Smillie, L. B. (1981) J. Mol. Biol. 149, 541-550). With beta-tropomyosin from rabbit skeletal muscle and with tropomyosins from equine platelets and chicken gizzard, the binding of fragment T1 was not observed at 0.1 M NaCl, while that for T2 was the same as for rabbit skeletal alpha-tropomyosin and remained Ca2+-sensitive in the presence of troponin-C. In the case of bovine aorta tropomyosin, neither T1 nor T2 was bound under these conditions.
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PMID:Binding of troponin-T fragments to several types of tropomyosin. Sensitivity to Ca2+ in the presence of troponin-C. 710 28

A differential scanning calorimeter was used to observe thermally induced conformational transitions in subfragment 2 (S-2) of myosin. In addition to an endotherm for the major transition which had been observed by several other methods earlier, a small broad endotherm was noted with a Tm of 41 degrees C. By analysis of the heat capacity profiles of long and short S-2, this endotherm was assigned to the hinge region. Comparison of the amino acid compositions of S-2 and tropomyosin showed them to be remarkably similar, and in view of their similar behavior in calorimetric studies, it is apparent that interactions stabilizing the coiled-coil structure of S-2 are a hydrophobic interface supported by charged interaction spanning the groove as was suggested for tropomyosin by McLachlan and Stewart [McLachlan, A. D., & Stewart, M. (1975) J. Mol. Biol. 98, 293-304].
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PMID:Conformational transitions in the subfragment-2 region of myosin. 744 75


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