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PubMed1998

A structural scaffolding of intermediate filaments in health and disease.

The cytoplasm of animal cells is structured by a scaffolding composed of actin microfilaments, microtubules, and intermediate filaments. Intermediate filaments, so named because their 10-nanometer diameter is intermediate between that of microfilaments (6 nanometers) and microtubules (23 nanometers), assemble into an anastomosed network within the cytoplasm. In combination with a recently identified class of cross-linking proteins that mediate interactions between intermediate filaments and the other cytoskeletal networks, evidence is reviewed here that intermediate filaments provide a flexible intracellular scaffolding whose function is to structure cytoplasm and to resist stresses externally applied to the cell. Mutations that weaken this structural framework increase the risk of cell rupture and cause a variety of human disorders.

Animals↗
PubMed1998

Identification and characterization of RNA-binding activities of avian reovirus non-structural protein sigmaNS.

Cytoplasmic extracts prepared from avian reovirus (ARV) strain S1133-infected chicken embryo fibroblasts were examined for the presence of RNA-binding proteins in order to identify and characterize ARV RNA-binding proteins. Analysis of binding activity to poly(A)-Sepharose indicated that infected cells contained significant amounts of a protein that co-migrated with ARV protein sigmaNS present in total virus-infected cell extracts. Determination of the N-terminal amino acid sequence of several peptide fragments generated by V8 protease digestion of the poly(A)-Sepharose-purified protein confirmed that this viral protein was sigmaNS. Competition assays showed that single-stranded RNA from the unrelated avian pathogen infectious bursal disease virus was able to compete for binding of sigmaNS to poly(A)-Sepharose. These data suggest that ARV sigmaNS binds to single-stranded RNA in a nucleotide sequence non-specific manner and is functionally similar to its counterpart specified by mammalian reovirus.

Animals↗
PubMed1988

Bluetongue virus tubules made in insect cells by recombinant baculoviruses: expression of the NS1 gene of bluetongue virus serotype 10.

Bluetongue virus (BTV) forms tubules in mammalian cells. These tubules appear to be composed of only one type of protein, NS1, a major nonstructural protein of the virus. To obtain direct evidence for the origin of the tubules, the complete M6 gene of BTV serotype 10 was inserted into the baculovirus transfer vector pAcYM1, so that it was under the control of the polyhedrin promoter of Autographa californica nuclear polyhedrosis virus. After cotransfection of Spodoptera frugiperda cells with wild-type A. californica nuclear polyhedrosis virus DNA in the presence of recombinant transfer vector DNA, polyhedrin-negative baculoviruses were recovered. When S. frugiperda cells were infected with one of the derived recombinant viruses, a protein similar in size and antigenic properties to the authentic BTV NS1 protein was made (representing ca. 50% of the stained cellular proteins). The protein reacted with BTV antibody and formed numerous tubular structures in the cytoplasm of S. frugiperda cells. The tubular structures have been purified to homogeneity from infected-cell extracts by gradient centrifugation. By enzyme-linked immunosorbent assay, the recombinant virus antigen has been used to identify antibodies to five United States BTV serotypes in infected sheep sera, indicating the potentiality of the expressed protein as a group-reactive antigen in the diagnosis of BTV infections.

Animals↗
PubMed1990

Morphology of griseofulvin-resistant isolates of Mongolian variant of Trichophyton schoenleini.

Clinical, experimental and electronmicroscopic observations, and computer-enhanced images were made on 5 patients with tinea favosa resistant to griseofulvin. The pathologic fungus was identified as the Mongolian variant of Trichophyton schoenleini. The results of physical examinations, routine tests of blood, urine and stool, liver and immunologic function examinations were normal in all of the 5 patients. Under scanning electron microscopy, the surface of the spore showed pineapple-like form, the cluster of the acrogenous spores presented flower shape, and the antler-like hyphae appeared twisted in the culture. They were observed by transmission electron microscope and the images were processed by microcomputer. It was found that the cell walls of the fungi consisted of 8 layers, among which the inner layer was loose and contained cytoplasm. It was also found that all structures within the cytoplasm possessed a 1-3 layer intact envelope and there was chromatin in the nucleus. These may be contributing factors in the development of resistance to griseofulvin. This multiple-layered thick cell wall may act as a barrier responsible for the impermeability of the cell of fungi to griseofulvin.

Adolescent↗
PubMed1994

Structural requirements of Bacillus subtilis small cytoplasmic RNA for cell growth, sporulation, and extracellular enzyme production.

Bacillus subtilis small cytoplasmic RNA (scRNA; 271 nucleotides) is a member of the signal recognition particle (SRP) RNA family, which has evolutionarily conserved primary and secondary structures. The scRNA consists of three domains corresponding to domains I, II, and IV of human SRP 7S RNA. To identify the structural determinants required for its function, we constructed mutant scRNAs in which individual domains or conserved nucleotides were deleted, and their importance was assayed in vivo. The results demonstrated that domain IV of scRNA is necessary to maintain cell viability. On the other hand, domains I and II were not essential for vegetative growth but were preferentially required for the RNA to achieve its active structure, and assembled ribonucleoprotein between Ffh and scRNA is required for sporulation to proceed. This view is highly consistent with the fact that the presence of domains I and II is restricted to sporeforming B. subtilis scRNA among eubacterial SRP RNA-like RNAs.

Bacillus subtilis↗
PubMed1997

Subcellular localization of the 28 kDa protein of the triple-gene-block of bamboo mosaic potexvirus.

Open reading frame 2 of the bamboo mosaic potexvirus (BaMV) genome encodes a 28 kDa protein, the first of the "triple-gene-block' of BaMV which is believed to play a role in cell-to-cell movement of the virus in host plants. The 28 kDa protein was expressed in Escherichia coli and polyclonal antiserum was raised in a rabbit. Western blot analyses showed that the 28 kDa protein was associated mainly with components in the cell wall and 30000 g pellet fractions of a BaMV-infected leaf homogenate. Immunogold electron microscopy of infected leaf tissues revealed that the 28 kDa protein was associated with electron-dense crystal-line bodies (EDCBs) in the cytoplasm and nuclei. Nuclear EDCBs were found closely associated with nucleoli. Gold-labelled EDCB-like structures were also detected in the cytoplasm, but not within nuclei, in protoplasts up to 48 h post-inoculation. No specific labelling of the 28 kDa protein was found within any cytoplasmic structures or within cell walls.

Animals↗
PubMed2002

Identification of a critical ankyrin-binding loop on the cytoplasmic domain of erythrocyte membrane band 3 by crystal structure analysis and site-directed mutagenesis.

The cytoplasmic domain of erythrocyte membrane band 3 (cdb3) serves as a center of membrane organization, interacting with such proteins as ankyrin, protein 4.1, protein 4.2, hemoglobin, several glycolytic enzymes, a tyrosine phosphatase, and a tyrosine kinase, p72(syk). The crystallographic structure of the cdb3 dimer has revealed that residues 175-185 assume a beta-hairpin loop similar to a putative ankyrin-binding motif at the cytoplasmic surface of the Na(+)/K(+)-ATPase. To test whether this hairpin loop constitutes an ankyrin-binding site on cdb3, we have deleted amino acids 175-185 and substituted the 11-residue loop with a Gly-Gly dipeptide that bridges the deletion without introducing strain into the structure. Although the deletion mutant undergoes the same native conformational changes exhibited by wild type cdb3 and binds other peripheral proteins normally, the mutant exhibits no affinity for ankyrin. This suggests that the exposed beta-hairpin turn indeed constitutes a major ankyrin-binding site on cdb3. Other biochemical studies suggest that ankyrin also docks at the NH(2) terminus of band 3. Thus, antibodies to the NH(2) terminus of cdb3 block ankyrin binding to the cdb3, and ankyrin binding to cdb3 prevents p72(syk) phosphorylation of cdb3 at its NH(2) terminus (predominantly at Tyr-8). However, a truncation mutant of cdb3 lacking the NH(2)-terminal 50 residues displays the same binding affinity as wild type cdb3. These data thus suggest that the NH(2) terminus of cdb3 is proximal to but not required for the cdb3-ankyrin interaction.

Amino Acid Motifs↗
PubMed2002

Solution structure and backbone dynamics of the functional cytoplasmic subdomain of human ephrin B2, a cell-surface ligand with bidirectional signaling properties.

The cytoplasmic domain of B ephrins plays a central role in bidirectional signal transduction processes controlling pattern formation and morphogenesis, such as axon guidance, cell migration, segmentation, and angiogensis. In particular, the extremely conserved last 33-residue cytoplasmic subdomain was shown to bind to both a PDZ domain for one signaling pathway [Lu et al. (2001) Cell 105, 69-79] and an SH2 domain from an alternative signaling network [Cowan and Henkemeyer (2001) Nature 413, 174-179]. To date, no structural information is available for the cytoplasmic domain of ephrin B proteins. We report here a detailed NMR study on the structural and dynamic properties of the cytoplasmic domain of human ephrin B2. Our results reveal the following: (1) the N-terminal region of the cytoplasmic domain from residues 253 to 300 lacks the ability for structure formation and is particularly prone to aggregation; and (2) the C-terminal functional subdomain from residues 301 to 333 assumes two distinctive structural elements with residues 301-322 adopting a well-packed hairpin structure followed by a flexible C-terminal tail. Furthermore, the backbone (15)N relaxation data demonstrate that the hairpin structure has significantly limited backbone motions, indicating a high conformational stability for the folded structure. Therefore, while the flexible C-terminal tail is suitable for binding to the PDZ domain, the folded hairpin may represent a latent structure requiring phosphorylation-induced conformational changes for high-affinity interactions with the SH2 domain.

Amino Acid Sequence↗
PubMed1988

Appearance of membranocystic lesion (Nasu)-like changes in Behçet's syndrome. An electron microscopic study of erythema nodosum-like lesions.

Membranocystic lesion (Nasu)-like changes were seen in the subcutaneous fat tissues of erythema nodosum-like lesions in three of 18 patients with Behçet's syndrome. The membranocystic structures, which were derived from degenerative fat cells with a loss of the cell membrane, were observed in the edematous connective tissues accompanied by fibrin deposition and diapedesis of erythrocytes. Electron microscopic evaluation revealed two different patterns of peculiar membranous structures in the cytoplasm of the degenerative fat cells. One was proliferating membrane structures such as well developed Golgi-endoplasmic reticulum, and the other was minute tubular structures such as intracytoplasmic microvesicles. These degenerative fat cells are considered to be derived from abnormal fat cells which lack a cell membrane, but whose cellular and nuclear configurations appear to be normal morphologically, because the cytoplasm of these abnormal cells showed the same tubular structures as those seen in the characteristic architecture of membranocystic lesion-like change. The relation between the appearance of such abnormal cells and the pathologic conditions of erythema nodosum-like lesions in Behçet's syndrome was discussed.

Adipose Tissue↗
PubMed1993

The nuclear pore complex: three-dimensional surface structure revealed by field emission, in-lens scanning electron microscopy, with underlying structure uncovered by proteolysis.

The structure of the nuclear pore complex (NPC) has been previously studied by many different electron microscopic techniques. Recently, scanning electron microscopes have been developed that can visualise biologically relevant structural detail at the same level of resolution as transmission electron microscopes and have been used to study NPC structure. We have used such an instrument to visualise directly the structure of both cytoplasmic and nucleoplasmic surfaces of the NPC of manually isolated amphibian oocyte nuclear envelopes that have been spread, fixed, critical point dried and coated with a thin fine-grained film of chromium or tantalum. We present images that directly show features of the NPC that are visible at each surface, including coaxial rings, cytoplasmic particles, plug/spoke complexes and the nucleoplasmic basket or fishtrap. Some cytoplasmic particles are rod-shaped or possibly "T"-shaped, can be quite long structures extending into the cytoplasm and may be joined to the coaxial ring at a position between each subunit. Both coaxial rings, which are proud of the membranes, can be exposed by light proteolytic digestion, revealing eight equal subunits each of which may be bipartite. We have determined that the nucleoplasmic filaments that make up the baskets are attached to the outer periphery of the coaxial ring at a position between each of its subunits. These filaments extend into the nucleoplasm and insert at the distal end to the smaller basket ring. The space left between adjacent basket filaments would exclude particles bigger than about 25 nm, which is consistent with the exclusion limit previously found for NPC-transported molecules.

Actin Cytoskeleton↗
PubMed1991

Solitary myeloma with massive extracellular crystalline structures--a case report.

We describe a case of solitary myeloma showing cystic change filled with massive crystalline structures in a 54-year-old woman. A bone X-ray showed a solitary cystic osteolytic lesion in the right iliac bone. Serum and urine protein electrophoresis showed no demonstrable M-protein, and bone-marrow aspirates did not show any myeloma cells. Histologic examination of the tumor revealed aggregation of plasma cells with massive extracellular infiltration of the rhomboid-shaped crystalline structures. In immunoperoxidase staining, both these crystalline structures and the cytoplasms of the myeloma cells demonstrated a positive reaction for lambda light chain. By electron microscope, the large extracellular crystalline structures were observed, and we found unique rhomboid or rectangular-shaped crystalline structures in the cytoplasms of the myeloma cells.

Bone Neoplasms↗
PubMed2003

[Basic types and vital forms of human peripheral and PHA-stimulated lymphocytes studied in vitro].

Natural diversity in peripheral and PHA-stimulated lymphocytes seen in the same donors was studied using digitized streak photo of living cells in observational camera. Cells were monitored for 5-8 h at the superior limit of optical resolution by means of phase-contrast microscopy. Intact lymphocytes were observed in autological blood plasma, and PHA-stimulated lymphocytes were examined in self-conditioned centrifuged growth medium. The majority of intact cells were small- and middle-sized floating lymphocytes with microvilli, and middle-sized caudate lymphocytes capable of stick-slip motion. The lesser part consisted of "spread-eagle" or movable forms of both large granular lymphocytes and middle-sized lymphocytes of several types: narrow-plasm lymphocytes with lamellipodia, wide-plasm lymphocytes without cytoplasmic processes, lymphocytes with single pseudopodia, and lymphocytes with single lobopodia of complex shape. On the contrary, the minor fraction of PHA-stimulated lymphocytes of 3 day old cultures contained floating cells with microvilli or floating cells with microvilli and two pseudopodia, whereas the majority of these lymphocytes were spread-eagle or movable forms of cells of different type. These substrate-adhesive PHA-stimulated lymphocytes had well defined apical and basal cell surfaces, but upon mechanical stress are easily pinched off to become ball-shaped. At least 6 different cell types were distinguished among substrate-adhesive PHA-stimulated lymphocytes, with more than half of these being heavily vacuolated spheroid lymphocytes prone to forming cell clusters. The rest PHA-stimulated lymphocytes were represented by signet-ring lymphocytes with dark or light cytoplasm, narrow-plasm lymphocytes with large prolonged nuclei and lamellipodia, lymphocytes with single lobopodia, and lymphocytes with single spiral structures in the cytoplasm. The spiral structure is 10-11 microns in length and 0.5-0.7 micron in width, being presumably a mitochondrion or a group of butt-joined mitochondria. Since some of the caudate middle-sized lymphocytes also contain this structure, these may be regarded as putative precursors of respective type of PHA-stimulated lymphocytes. Under the conditions of observation, interphase nuclei of all live PHA-stimulated lymphocytes were seen to contain numerous globular or fiber structures of condensed chromatin made of 0.3-0.8 micron beads. These beads are doubtless interphase chromomeres.

Cell Nucleus↗
PubMed2004

Mammalian GRIP domain proteins differ in their membrane binding properties and are recruited to distinct domains of the TGN.

The four mammalian golgins, p230/golgin-245, golgin-97, GCC88 and GCC185 are targeted to trans-Golgi network (TGN) membranes by their C-terminal GRIP domain in a G-protein-dependent process. The Arf-like GTPase, Arl1, has been shown to mediate TGN recruitment of p230/golgin245 and golgin-97 by interaction with their GRIP domains; however, it is not known whether all the TGN golgins bind to Arl1 and whether they are all recruited to the same or different TGN domains. Here we demonstrate differences in membrane binding properties and TGN domain recruitment of the mammalian GRIP domain proteins. Overexpression of full-length GCC185 resulted in the appearance of small punctate structures dispersed in the cytoplasm of transfected cells that were identified as membrane tubular structures by immunoelectron microscopy. The cytoplasmic GCC185-labelled structures were enriched for membrane binding determinants of GCC185 GRIP, whereas the three other mammalian GRIP family members did not colocalize with the GCC185-labelled structures. These GCC185-labelled structures included the TGN resident protein alpha2,6 sialyltransferase and excluded the recycling TGN protein, TGN46. The Golgi stack was unaffected by overexpression of GCC185. Overexpression of both full-length GCC185 and GCC88 showed distinct and nonoverlapping structures. We also show that the GRIP domains of GCC185 and GCC88 differ in membrane binding properties from each other and, in contrast to p230/golgin-245 and golgin-97, do not interact with Arl1 in vivo. Collectively these results show that GCC88, GCC185 and p230/golgin245 are recruited to functionally distinct domains of the TGN and are likely to be important for the maintenance of TGN subdomain structure, a critical feature for mediating protein sorting and membrane transport.

ADP-Ribosylation Factors↗
PubMed1995

Characterization of sugar receptor expression by neoglycoproteins in oral and oropharyngeal squamous cell carcinomas.

Recognition of the carbohydrate part of cellular glycoconjugates by sugar receptors like lectins may contribute to biosignaling and interactions between normal and transformed cells. Such recognitions may be essential for establishing phenotypic characteristics in neoplastic cells, including metastasis-associated properties. To evaluate various glycoconjugates in tumor diagnosis and clinical therapy, a panel of 18 biotinylated neoglycoproteins was prepared. This included conjugates of a histochemically inert carrier protein and crucial sugar moieties such as D-glucuronic acid, alpha- and beta-N-acetyl-galactosamine, beta-N-acetyl-glucosamine, melibiose, lactose, maltose, cellobiose, mannose, mannose-6-phosphate, fucose, rhamnose, and xylose. In so doing the diazo derivative of the respective p-aminophenyl glycosides was coupled with galactose, beta-N-acetyl-galactosamine or beta-N-acetyl-glucosamine via an epoxy group-containing aliphatic spacer. Other glycoconjugates used were the proteoglycan heparin and the sulfated fucan fucoidan. Labeling was effected with cyanogen bromide activation and aminoalkylation for specific detection of endogeneous sugar receptors, especially lectins. Tissues studied were paraformaldehyde-fixed, paraffin-embedded surgical biopsies from patients with different stages of squamous cell carcinomas (SCCs) of the oral cavity (n = 16) and oropharynx (n = 17), including three lymph node metastases from oropharyngeal primary tumors. Semiquantitative binding differences of probes to tumor stages were evaluated statistically by the Mann-Whitney U-Wilcoxon rank sum W test. Specific binding of a probe to cytoplasmic and nuclear structures was detected with apparent quantitative differences. Overall, the cytoplasmic compartment revealed a higher intensity of histochemical reaction than did nuclear structures, indicating a comparatively higher density of specific carbohydrate receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Complementary DNA cloning and kinetic characterization of a novel intracellular serine proteinase inhibitor: mechanism of action with trypsin and factor Xa as model proteinases.

The full-length cDNA encoding a novel human intracellular serine proteinase inhibitor has been sequenced and found to encode a 376 amino acid protein (M(r) approximately 42.5K) that we designate as cytoplasmic antiproteinase. Analysis of the primary structure revealed that the cytoplasmic antiproteinase has the majority of structural motifs conserved among the greater superfamily of serine proteinase inhibitors, or serpins. On the basis of several criteria such as amino acid identity and the absence of a classical N-terminal signal peptide, the cytoplasmic antiproteinase represents a new member of the intracellular serpin family. Further inspection of the cytoplasmic antiproteinase amino acid sequence identified three potential N-glycosylation sites and Arg341-Cys342 as the reactive site P1-P1' residues, respectively. We have also employed the slow binding kinetic approach to detail the mechanism of bovine trypsin and human factor Xa inhibition by the novel cytoplasmic antiproteinase. Inhibition of trypsin by the cytoplasmic antiproteinase was preceded by a two-step mechanism corresponding to the formation of an initial loose complex, followed by an isomerization step to a more stable, tight complex. The binding of the cytoplasmic antiproteinase to trypsin occurred with a second-order association rate constant of 2.8 x 10(6) M-1 s-1 and an overall equilibrium constant of 22.5 pM, demonstrating that the factor is a potent inhibitor of this proteinase. Under the appropriate conditions, the tight complex between trypsin and the cytoplasmic inhibitor was reversible, indicated by an exponential regeneration of proteinase amidolytic activity from the preformed complex. Therefore, the tight complex appears to be stabilized predominantly by reversible bonds that form between trypsin and the cytoplasmic inhibitor. In contrast to the inhibition of trypsin, the inhibition of factor Xa amidolytic activity by the cytoplasmic antiproteinase followed a single-step binding mechanism. The apparent first-order rate constant for factor Xa inhibition was found to increase as a linear function of the inhibitor concentration range studied. Formation of the inhibitory complex between factor Xa and the cytoplasmic antiproteinase occurred with a second-order association rate constant of approximately 1.3 x 10(5) M-1 s-1 and a equilibrium constant of 3.7 nM. These findings suggests that the cytoplasmic inhibitor may initially encounter significant energy barriers for proper alignment with the substrate binding cleft of factor Xa. However, once aligned, the reaction proceeds rapidly to a tight factor Xa.inhibitor complex that dissociates at a slow rate.

Amino Acid Sequence↗
PubMed2004

Morphological evidences for onion-induced growth inhibition of Trichophyton rubrum and Trichophyton mentagrophytes.

The antifungal activity of onion (Allium cepa L.) on two important dermatophytes, Trichophyton rubrum and Trichophyton mentagrophytes, with special reference to morphological aspects was studied. Growth of both fungi was found to be strongly inhibited by aqueous onion extract (AOE) as a dose-dependent manner. The extract showed fungicidal effect for both fungi at concentrations >3.12% (v/v). The fungus T. mentagrophytes was more affected by the onion as compared to T. rubrum at all concentrations used. Morphological effects of onion exposure were examined in correlation with fungal growth. Corresponding to the growth inhibition, light and electron microscopy observations revealed morphological anomalies in hyphal compartments. The results demonstrated that AOE targets the cell membrane of the fungi as breaking down of both inner and outer membranes with consequent extrution of materials into the surrounding medium. Cytoplasmic membranes and other membranous structures of organelles, such as nuclei and mitochondria, were also disrupted. In correlation to the fungal growth, morphological alterations occurred to a less content for T. rubrum compared with T. mentagrophytes. The hyphae of T. rubrum were found to be mainly affected by converting to resistant forms, i.e., chlamidospores as a consequence of phenotype switching response to AOE. Plasmolysis accompanied by an almost complete depletion and disorganization of cytoplasmic structures were found to be the final event which led to cell death. Ultrastructural evidences obtained from this study strongly support that morphological changes of T. rubrum and T. mentagrophytes caused by AOE are associated with its fungistatic and fungicidal activities. With respect to the morphological results and the preliminary data on fungal biochemistry, a mechanism of action by interacting of AOE with thiol (-SH) groups present in essential compartments of the fungal cells was postulated.

Antifungal Agents↗
PubMed2001

Structural and functional dissection of the cytoplasmic domain of the transmembrane adaptor protein SIT (SHP2-interacting transmembrane adaptor protein).

SIT (SHP2-interacting transmembrane adaptor protein) is a recently identified transmembrane adaptor protein, which is expressed in lymphocytes. Its structural properties, in particular the presence of five potential tyrosine phosphorylation sites, suggest involvement of SIT in TCR-mediated recruitment of SH2 domain-containing intracellular signaling molecules to the plasma membrane. Indeed, it has recently been demonstrated that SIT inducibly interacts with the SH2-containing protein tyrosine phosphatase 2 (SHP2) via an immunoreceptor tyrosine-based inhibition motif (ITIM). Moreover, SIT is capable to inhibit TCR-mediated signals proximal of activation of protein kinase C. However, inhibition of T cell activation by SIT occurs independently of SHP2 binding. The present study was performed to further characterize the molecular interaction between SIT and intracellular effector molecules and to identify the protein(s) mediating its inhibitory function. We demonstrate that SIT not only interacts with SHP2 but also with the adaptor protein Grb2 via two consensus YxN motifs. However, mutation of both Grb2-binding sites also does not influence the inhibitory function of SIT. In contrast, mutation of the tyrosine-based signaling motif Y(168) ASV completely abrogates the ability of SIT to inhibit T cell activation. Co-precipitation experiments revealed that the tyrosine kinase p50(csk) could represent the negative regulatory effector molecule that binds to this motif.

Adaptor Proteins, Signal Transducing↗