Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
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We have reported previously that rabbit skeletal myosin subfragment-1 (S-1) assembles actin filaments into bundles. The rate of this reaction can be estimated roughly from the initial rate (Vo) of the accompanying turbidity increase ("super-opalescence") of the acto-S-1 solution. Vo is a function of the molar ratio (r) of S-1 to actin, with a peak at r = 1/6 to 1/7 and minimum around r = 1. In the present paper we report a different type of opalescence (we call it "hyper-opalescence") of acto-S-1 solutions, which also resulted from bundle formation. Adjacent filaments in the bundles had a distance of approximately 180 A. Hyper-opalescence occurred at r approximately equal to 1 when KCOOCH3 was used instead of KCl. By comparing the effects of ADP, epsilon-ADP, tropomyosin or ionic strength upon the super- and hyper-opalescence, we concluded that the two types of S-1-induced actin bundling had different molecular mechanisms. The hyper-opalescence type of bundling seemed to be induced by S-1, which was not complexed with actin in the manner of conventional rigor binding. The presence of the regulatory light chain did not affect hyper-opalescence (or super-opalescence), since there were no significant differences between papain S-1 and chymotryptic S-1 with respect to these phenomena.
J Mol Biol 1987 May 20
PMID:Bundling of myosin subfragment-1-decorated actin filaments. 365 17

Ca2+ binding to troponin C (TnC), a subunit of the thin filament regulatory strand, activates vertebrate skeletal muscle contraction. Tension, however, increases with Ca2+ too abruptly to be the result of binding to sites on individual TnCs. Because extraction of one TnC on average per regulatory strand dramatically reduces the slope of the tension/Ca2+ relationship, we proposed that all 26 troponin-tropomyosin complexes of the regulatory strand form a co-operative system. This study of permeabilized (chemically skinned) rabbit psoas fibers analyzes the extraction time-course, the distribution of extraction sites on regulatory strands and the effects of extraction on the co-operativity of the tension/Ca2+ relationship. Two components of TnC are resolved in the time-course of extraction: a "rapidly extracting" component that can be selectively removed without affecting tension or co-operativity, and a "slow extracting" component whose loss reduces tension and co-operativity. Extraction of [14C]TnC shows that the slowly extracting component is lost randomly, so that, after removal of 5% of the TnC, most extracted strands have lost one TnC. Extraction interrupts the transmission of co-operativity by dividing the regulatory strand into smaller, independent co-operative systems; it reduces tension by preventing Ca2+ activation of TnC-depleted regulatory units. Co-operativity of the tension/Ca2+ relationship is modeled with the concerted-transition formalism for intact systems of 26 regulatory units, and for the smaller systems in extracted fibers.
J Mol Biol 1987 Jun 20
PMID:Co-operative interactions between troponin-tropomyosin units extend the length of the thin filament in skeletal muscle. 365 37

The pattern given by contracting frog muscle can be followed with high time resolution using synchrotron radiation as a high-intensity X-ray source. We have studied the behaviour of the second actin layer-line (axial spacing of approximately 179 A) at an off-meridional spacing of approximately 0.023 A-1, a region of the diagram that is sensitive to the position of tropomyosin in the thin filaments. In confirmation of earlier work, we find that there is a substantial increase in the intensity of this part of the pattern during contraction. We find that the reflection reaches half its final intensity about 17 milliseconds after the stimulus at 6 degrees C. The changes in the equatorial reflections, which arise from movement of crossbridges towards the thin filaments, occur with a delay of about 12 to 17 milliseconds relative to this change in the actin pattern. In over-stretched muscle, where thick and thin filaments no longer overlap, the changes in the actin second layer-line still take place upon stimulation with a time course and intensity similar to that observed at full overlap. This indicates that tropomyosin movement, in response to calcium binding to troponin, is the first structural step in muscular contraction, and is the prerequisite for myosin binding. A change in intensity similar to that found in contracting muscle is seen in rigor, where tropomyosin is probably locked in the active position. During relaxation the earlier stages in the decrease in intensity of the second actin layer-line take place significantly sooner after the last stimulus than tension decay. In over-stretched muscles the intensity decay is appreciably faster than in the same muscles at rest length, where attached crossbridges may interfere with the return of tropomyosin to its resting position.
J Mol Biol 1986 Apr 05
PMID:Structural changes during activation of frog muscle studied by time-resolved X-ray diffraction. 373 25

Functional properties of the protein complex from bovine brain that shortens actin filaments are described. In the presence of Ca2+ complex shortens actin filaments and increases the initial rate of actin polymerization. In the absence of free calcium ions the complex loses its accelerating effect on actin polymerization, but still possesses actin filament shortening activity. Neither phalloidin nor tropomyosin prevent the shortening of actin filaments induced by the protein complex. Therefore the protein complex causes the fragmentation of actin filament. The data on actin polymerization in the presence of F-actin nuclei have indicated that the protein complex inhibits the elongation step of actin polymerization. The analysis of elongation in the presence of both the protein complex and cytochalasin D has demonstrated that the inhibition occurs on the fast-growing end of actin filaments.
Mol Biol (Mosk)
PMID:[Study of a protein complex from the brain which reduces actin viscosity. II. The complex inhibits elongation of actin filaments at the end preferable for polymerization and fragments the filaments]. 376 34

We identified six tropomyosin (Tm) isoforms in diploid human fibroblasts. We used computerized microdensitometry of 2-dimensional protein profiles to measure the relative rates of synthesis and abundance of the individual Tm isoforms and actin, the two major structural constituents of microfilaments. In carcinogen-transformed human fibroblasts (HuT-14), the rates of synthesis of three Tm isoforms (Tm1, Tm2, and Tm6) were greatly decreased relative to normal diploid parental fibroblasts and to actin. In contrast, related nontumorigenic HuT fibroblasts which are "immortalized" and anchorage independent exhibited both slight down-regulation of Tm1 and Tm6 and 3.5-fold up-regulation of Tm3. Thus, Tm isoform switching from the predominance of the larger more avid Tm isoforms (Tm1, Tm2, Tm3, and Tm6) to the smaller, less avid Tm isoforms (Tm4 and Tm5) in microfilaments was a transformation-induced change correlated with tumorigenicity in human fibroblasts.
Mol Cell Biol 1986 Jul
PMID:Tropomyosin isoform switching in tumorigenic human fibroblasts. 378 8

The crystal structure of tropomyosin filaments has been solved to 15 A resolution by refinement of models against the diffraction data and heavy atom labeling of cysteine residues. These results confirm and extend earlier findings. The improved maps reveal the pitch of the coiled coil, the location of the cysteine residues, and the location and features of the overlapping molecular ends in the filaments. A correlation can now be made between regions of the amino acid sequence and key features of the molecule, such as contact sites in the lattice and departures from regularity along the coiled coil. The crystal shows remarkable dynamic features and the relative flexibility of different parts of the molecule as well as its anisotropic character have been determined. The structure and motions of tropomyosin in the crystal provide information on the structure of tropomyosin in muscle and its possible role in regulation. An atomic model of the molecule has been constructed, based on the low resolution X-ray results, together with the stereochemistry of alpha-helical coiled coils. In contrast to previous views, the molecule appears to display but one set of seven alpha-sites that permit weak linkages of the flexible tropomyosin filament to the actin helix. Correspondingly, we picture that in the "off" state of ATPase activity, the alpha-sites are not occupied; in the "on" state, they are only partly occupied; and in the "potentiated" state, they are more completely saturated. Control of contraction is therefore seen as a statistical mechanism requiring at least three distinct average conformations for the tropomyosin molecule on the actin helix.
J Mol Biol 1986 Nov 05
PMID:Tropomyosin crystal structure and muscle regulation. 382 Feb 99

We have carried out a detailed analysis of tropomyosin structure using lysines as specific probes for the protein surface in regions of the molecule that have not been investigated by other methods. We have measured the relative reactivities of lysines in rabbit skeletal muscle alpha, alpha-tropomyosin with acetic anhydride using a competitive labeling procedure. We have identified 37 of 39 lysines and find that they range 20-fold in reactivity. The observed reactivities are related to the coiled-coil model of the tropomyosin molecule [Crick, F.H.C. (1953) Acta Crystallogr. 6, 689-697; McLachlan, A.D., Stewart, M., & Smillie, L.B. (1975) J. Mol. Biol. 98, 281-291] and other available chemical and physical information about the structure. In most cases, the observed lysine reactivities can be explained by allowable interactions with neighboring amino acid side chains on the same or facing alpha-helix. However, we found no correlation between reactivity and helical position of a given lysine. For example, lysines in the outer helical positions included lysines of low as well as high reactivity, indicating that they vary widely in their accessibility to solvent and that the coiled coil is heterogeneous along its length. Furthermore, the middle of the molecule (residues 126-182) that is susceptible to proteolysis and known to be the least stable region of the protein also contains some of the least and most reactive lysines. We have discussed the implications of our results on our understanding the structures of tropomyosin and other coiled-coil proteins as well as globular proteins containing helical regions.
 ...
PMID:Tropomyosin lysine reactivities and relationship to coiled-coil structure. 392 77

To identify proteins whose production may be altered as a common event in the expression of structurally diverse oncogenes, we compared two-dimensional electropherograms of newly synthesized proteins from NIH/3T3 cell lines transformed by a variety of retroviral oncogenes, from cellular revertant lines, and from a line (433.3) which expresses the v-ras oncogene in response to corticosteroids. Most alterations in the synthesis of specific proteins detected by this approach appeared to be the result of selection during prolonged cultivation and were probably unrelated to the transformation process. However, we detected seven proteins whose synthesis was strongly suppressed in cell lines transformed by each of the six retroviral oncogenes we studied and whose production was fully or partially restored in two cellular revertant lines. Suppression of two of these proteins was also correlated with the initial appearance of morphological alteration during corticosteroid-induced oncogene expression in 433.3 cells. These proteins (p37/4.78 and p41/4.75) were identified as tropomyosins, a group of at least five cytoskeletal proteins. Transformation by the papovaviruses simian virus 40 and polyomavirus caused no suppression of synthesis of these tropomyosins. This indicates that suppression of tropomyosin synthesis is not a nonspecific response by cells to being forced to grow with the transformed phenotype but is specifically associated with oncogenesis by diverse retroviral oncogenes. The results are consistent with the hypothesis that the different biochemical processes initiated by expression of structurally diverse retroviral oncogenes may converge on a limited number of common targets, one of which is the mechanism which regulates the synthesis of tropomyosins.
Mol Cell Biol 1985 May
PMID:Suppression of tropomyosin synthesis, a common biochemical feature of oncogenesis by structurally diverse retroviral oncogenes. 400 Jan 23

The binding of cardiac actin and tropomyosin to a cardiotoxic antineoplastic agent, doxorubicin, and its covalently crosslinked derivatives was investigated. The primary amino group of the daunosamine moiety of doxorubicin was blocked with fluorescein isothiocyanate. This doxorubicin derivative did not bind to Sepharose which was conjugated with cardiac actin. A doxorubicin dimer was made by covalently crosslinking one doxorubicin molecule to another identical doxorubicin molecule through the free amino group of each daunosamine moiety. This derivative demonstrated mobility different from parent doxorubicin on thin-layer chromatography, different elution pattern by column chromatography, and did not show binding affinity for actin. Exploring other purified thin-filament proteins, it was found that doxorubicin did bind to tropomyosin when gel filtration was performed on the protein drug mixture. The ability of tropomyosin to form paracrystal in vitro was not disturbed by a variety of concentrations of doxorubicin. These data support the concept that the doxorubicin solitary free amino group is the site which is responsible for this ligand to bind to actin and may relate to its cardiotoxic effects.
Exp Mol Pathol 1985 Aug
PMID:Doxorubicin and covalently crosslinked doxorubicin derivatives binding to purified cardiac thin-filament proteins in vitro. 400 42

Arterial intima proteins were extracted by 9 M urea from matching histologically atheroma-free areas of 27 human thoracic aortas of both sexes from younger (15-34) and older (35-82) age groups and studied after separation by high-resolution two-dimensional polyacrylamide gel electrophoresis. Seventeen specific protein groups on each gel were identified according to their relative charges and molecular weights and their distribution in the two age groups compared. Some plasma-derived proteins occurred rarely in young aortas while they were consistently found in those from older cases, i.e., protein group 4 (alpha 1-antichymotrypsin) 1/13 (8%) vs 12/14 (86%), group 7 (haptoglobin beta-chain) 1/13 (8%) vs 13/14 (93%) and groups 6 and 9 (IgG chains) 3/13 (23%) vs 9/14 (64%), respectively. Other plasma-derived proteins such as group 3 (albumin) and 5 (alpha 1-antitrypsin) were identified in all samples of both age groups but their expression in the aortic intima increased with age. Proteins which are typically found intracellularly such as those from groups 11 (actin), 12 (cytoskeleton proteins), and 13 (tropomyosin-like proteins) appeared in samples of intima of both age groups but were less apparent in older specimens. These studies suggest that the changes in aortic intima protein distribution in the absence of atherosclerosis closely correlate with histological changes such as intimal thickening often found with aging, providing new sensitive markers of vascular senescence.
Exp Mol Pathol 1985 Dec
PMID:Effect of aging on human aortic protein composition. II. Two-dimensional polyacrylamide gel electrophoretic analysis. 406 9


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