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At least 163 records · Page 9Linked to original sources
PubMed2003

The GW182 protein colocalizes with mRNA degradation associated proteins hDcp1 and hLSm4 in cytoplasmic GW bodies.

A novel cytoplasmic compartment referred to as GW bodies (GWBs) was initially identified using antibodies specific to a 182-kD protein termed GW182. GW182 was characterized by multiple glycine(G)-tryptophan(W) repeats and an RNA recognition motif (RRM) that bound a subset of HeLa cell messenger RNAs (mRNAs). The function of GWBs was not known; however, more recent evidence suggested similarities between GWBs and cytoplasmic structures that contain hLSm proteins and hDcp1, the human homolog to a yeast decapping enzyme subunit. In this study, we used antibodies to hLSm4 and hDcp1 to show that both of these markers of an mRNA degradation pathway colocalize to the same structures as GW182. Our studies demonstrate that GW182, hLSm4, and hDcp1 are found in the same cytoplasmic structures and suggest that GW182 is involved in the same mRNA processing pathway as hLSm4 and hDcp1.

Autoantigens↗
PubMed1983

The protein responsible for the repeating structure of cytoplasmic poly(A)-ribonucleoprotein.

A 75,000-dalton protein has been purified approximately 1,000-fold from rat liver, based on its capacity to organize poly(A) in a 27-residue repeating structure. This protein may be identified with the major polypeptide component of cytoplasmic poly(A)-ribonucleoprotein (RNP) previously described. The poly(A)-organizing activity of the protein is detected only in cytoplasmic fractions. Upon nuclease digestion of the 75,000-dalton protein-poly(A) complex, monomers, and higher multimers of RNP subunits can be resolved in a sucrose gradient. The sedimentation rate of the monomer is compatible with a composition of one 75,000-dalton protein molecule and one 27-residue segment of poly(A).

Animals↗
PubMedDate not supplied

[Structure of cytoplasmic glycerol-3-phosphate dehydrogenase in experimental atherosclerosis in rabbits].

Differences in the ratio of molecular forms of crystalline glycerol-3-phosphate dehydrogenase (GPD, EC 1.1.1.8) from sceletal muscle and in their primary structure were found in rabbits with experimental atherosclerosis as compared with normal animals. In atherosclerosis the molecular weight of GPD and of its fragments was increased; the amino acid composition of these GPD molecules differs from that of control rabbits as shown by estimation of content of 8 amino acids. Experimental atherosclerosis is apparently related to alteration in the GPD primary structure.

Amino Acids↗
PubMed2001

Cytoplasmic surface structure of bacteriorhodopsin consisting of interhelical loops and C-terminal alpha helix, modified by a variety of environmental factors as studied by (13)C-NMR.

We have examined the (13)C-NMR spectra of [3-(13)C] Ala-labeled bacteriorhodopsin and its mutants by varying a variety of environmental or intrinsic factors such as ionic strength, temperature, pH, truncation of the C-terminal alpha helix, and site-directed mutation at cytoplasmic loops, in order to gain insight into a plausible surface structure arising from the C-terminal alpha helix and loops. It is found that the surface structure can be characterized as a complex stabilized by salt bridges or metal-mediated linkages among charged side chains. The surface complex in bacteriorhodopsin is most pronounced under the conditions of 10 mM NaCl at neutral pH but is destabilized to yield relaxed states when environmental factors are changed to high ionic strength, low pH and higher temperature. These two states were readily distinguished by associated spectral changes, including suppressed (cross polarization-magic angle spinning NMR) or displaced (upfield) (13)C signals from the C-terminal alpha helix, or modified spectral features in the loop region. It is also noteworthy that such spectral changes, when going from the complexed to relaxed states, occur either when the C-terminal alpha helix is deleted or site-directed mutations were introduced at a cytoplasmic loop. These observations clearly emphasize that organization of the cytoplasmic surface complex is important in the stabilization of the three-dimensional structure at ambient temperature, and subsequently plays an essential role in biological functions.

Amino Acid Sequence↗
PubMed1981

Cytoplasmic helical structure associated with Acholeplasma laidlawii.

A distinct spiral protein structure was found in three species of Acholeplasma, but was not found in the Mycoplasma species studied. The spirals, which are 14 nm in width and of variable length from 50 to 300 nm, are formed by a helical arrangement of 7-nm subunits. A rosette-like structure 45 nm in diameter also composed of 7-nm subunits was found in close association with the spirals and may be a taut in vivo form of the spiral. The electrophoretic profile in sodium dodecyl sulfate-polyacrylamide gels indicated that the spirals are composed of a predominant polypeptide with an apparent molecular weight of 100,000. No evidence can be found for inferring actin-like properties for this structure.

Acholeplasma↗
PubMed2002

Spermiophagy in the spermatheca of Melipona bicolor Lepeletier, 1836 (Hymenoptera, Apidae, Meliponini).

The presence of spermatozoa in vesicles in the cytoplasm of the epithelial cells that constitute the spermathecal wall of Melipona bicolor queen (Meliponini) is discussed in relation to the organ structure. The epithelial wall is lined by an apparently continuous cuticle in the luminal surface that should be a non-transposable barrier to the luminal spermatozoa. However, some spermatozoa were seen crossing the cuticle through interruptions that was first interpreted as sectioning defects. Nevertheless, the sperm cells in well-structured cytoplasmic vesicles, bound by membranes and sometimes associated to multivesicular bodies, as well as cytoplasmic structures representative of intracellular digestion and the occurrence of the phenomenon in two of the three spermathecae studied, suggest a real spermiophagic hole in the spermathecal epithelial cells.

Animals↗
PubMed2004

Endocytosis against high turgor: intact guard cells of Vicia faba constitutively endocytose fluorescently labelled plasma membrane and GFP-tagged K-channel KAT1.

The relevance of endocytosis in plants against high turgor pressure has frequently been questioned on the basis of energetic considerations. Here, we examine the dynamics of the plasma membrane (PM) in turgid guard cells of Vicia faba by monitoring with confocal microscopy the fate of fluorescent styryl dyes (FM1-43, FM2-10 and FM4-64). As a second marker, we also observe the retrieval of a fluorescent chimaera of the K(+)-inward rectifying channel from Arabidopsis thaliana and the green fluorescent protein (KAT1::GFP). Analysis of cytoplasmic structures, which became labelled by the different styryl dyes, revealed that only FM4-64, the most hydrophobic dye, was a reliable marker of endocytosis, whereas the two other styryl dyes resulted also in an unspecific labelling of different cytoplasmic structures including mitochondria. Over some minutes of incubation in continuous presence of these dyes, endocytic vesicles in the cortical cytoplasm beneath the PM were fluorescently labelled. The identification is based on the observation that the size distribution of these structures is very similar to that of endocytic vesicles obtained from patch-clamp capacitance recordings. Also, these structures are frequently co-labelled with KAT1::GFP. Taken together, the data show that turgid guard cells undergo vigorous constitutive endocytosis and retrieve membrane including the K(+)-channel KAT1 from the PM via endocytic vesicles.

Arabidopsis Proteins↗
PubMed1968

Autophagic vacuoles produced in vitro. I. Studies on cultured macrophages exposed to chloroquine.

Mouse macrophages exposed to 30 microg/ml of chloroquine in vitro develop autophagic vacuoles containing various cytoplasmic components and acid phosphatase. The early toxic vacuoles appear in the perinuclear region within 15 min; on electron microscopy, they show irregular shape, amorphous moderately dense content, apparent double membranes, and in some instances curved thin tubular extensions with a central, dark linear element. Cytoplasmic structures are probably transported into the vacuoles by invagination of the vacuolar membrane. After exposure to chloroquine for 1-4 hr, macrophages display large vacuoles containing degraded cytoplasmic structures, membranous whorls, and amorphous material. When chloroquine is removed by changing the culture medium after 4 hr, the cells survive and 24 hr later they exhibit no abnormality except for large cytoplasmic dense bodies packed with membrane lamellae. During recovery chloroquine disappears from the cells. 24 hr after exposure to chloroquine the macrophages have accumulated less hydrolases than control cells.

Acid Phosphatase↗
PubMed1995

Alpha 3 beta 1 and alpha 6 beta 1 integrins mediate laminin/merosin binding and function as costimulatory molecules for human thymocyte proliferation.

Integrins comprise a superfamily of alpha beta heterodimers that serve as cell signaling as well as adhesion molecules. We demonstrate that the alpha 3 beta 1 and alpha 6 beta 1 integrins are laminin/merosin receptors expressed in human thymocytes. By reverse transcriptase-PCR analysis, we determined that the alpha 3A beta 1, but not the alpha 3B beta 1, cytoplasmic structural variant of alpha 3 beta 1 is expressed in thymocytes. In contrast, both alpha 6A beta 1 and alpha 6B beta 1 cytoplasmic structural variants of alpha 6 beta 1 are expressed. A small percentage (10 to 15%) of human thymocytes bind to immobilized laminin, and even fewer (3 to 5%) bind to merosin, the laminin isoform normally present in the thymus. This binding, however, can be increased to 39 to 41% after activation of thymocytes with Mn2+ (or PMA). Binding to either laminin or merosin is completely inhibited by anti-beta 1 mAb or by a mixture of anti-alpha 3 and anti-alpha 6 mAbs, indicating that both alpha 3 beta 1 and alpha 6 beta 1 participate in thymocyte adhesion to the laminin family of extracellular matrix proteins. The protein kinase C inhibitors, calphostin C and staurosporine, inhibit Mn(2+)-enhanced thymocyte binding, suggesting that protein kinase C activity is crucial for the binding. Furthermore, the data indicate that at least two divalent cation binding sites serve to regulate integrin binding activity. Finally, we show that both immobilized laminin and merosin have costimulatory function for anti-CD3-induced thymocyte proliferation, and both anti-alpha 3 and anti-alpha 6 mAbs can block this proliferative response. The cooperative function of alpha 3 beta 1 and alpha 6 beta 1 evidenced in the laminin/merosin binding and proliferation assays suggests that thymocyte-merosin interactions may play an important role in thymic T cell development.

Base Sequence↗
PubMed1995

Conserved machinery of the bacterial flagellar motor.

Novel periplasmic and cytoplasmic structural modules of the bases of bacterial flagella have been observed in situ and isolated using new biochemical protocols. Flagellar rotation may depend upon interactions of these modules with the intramembrane particle rings, a ubiquitous feature of flagellar bases necessary for torque generation. The outer membrane-associated basal disk of the Wolinella succinogenes polar flagellum has architecture well suited for interaction with the ring particles. However, antibody against the main W. succinogenes basal disk protein did not cross-react with flagella-enriched fractions from Salmonella typhimurium and Bacillus firmus; nor have such structures been observed in these species thus far. Antibodies against two S. typhimurium proteins, FliG and FliM, known to be involved in motor function and part of the cytoplasmic module in this species cross-reacted with flagella-enriched fractions from both W. succinogenes and B. firmus. In addition, flagellar cytoplasmic structure could be isolated from B. firmus. The basal disk may anchor the flagellar motor to the cell wall in some polar bacteria, but this does not seem to be a unique strategy. In contrast, the data indicate that the cytoplasmic module is conserved.

Antigens, Bacterial↗
PubMed1995

Probing sodium channel cytoplasmic domain structure. Evidence for the interaction of the rSkM1 amino and carboxyl termini.

Epitopes for monoclonal antibodies directed against the purified adult rat skeletal muscle sodium channel (rSkM1) were localized using channel proteolysis and fusion proteins. The interactions between these and other monoclonal antibodies with site-specific polyclonal antibodies were used to investigate the spatial relationships among rSkM1 cytoplasmic segments. Competition. between antibodies for binding was performed using a solution-phase assay in which solubilized channel protein retains many of the biophysical characteristics of the rSkM1 protein in vivo. Our results support a model in which: 1) the amino terminus assumes a rigid structure having a fixed orientation with respect to other intracellular segments; 2) the interdomain 2-3 region is centrally located on the cytoplasmic surface of the channel, extends farther into the cytoplasm, and has an intermediate degree of flexibility; 3) the beginning of the amino terminus and end of the carboxyl terminus specifically interact with each other; and 4) domains 1 and 4 are adjacent. The sequences responsible for the interaction of the amino and carboxyl termini were identified by demonstrating the specific binding of a synthetic peptide encompassing the first 30 residues of the rSkM1 amino terminus to a fusion protein containing the rSkM1 carboxyl terminus.

Amino Acid Sequence↗