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PubMed2002

Co-crystallization of the human nuclear cap-binding complex with a m7GpppG cap analogue using protein engineering.

The nuclear cap-binding complex (CBC) binds the 7-methyl-G(5')ppp(5')N cap structure at the 5' end of pre-messenger and uracil-rich small nuclear RNAs in the nucleus. It mediates interaction of these capped RNAs with various nuclear machineries involved in RNA maturation and is co-exported with them to the cytoplasm. The structure of human CBC, which comprises the subunits CBP20 and CBP80, has previously been determined in a mildly trypsinated form which can no longer bind the cap. Here, the engineering and crystallization of two variant CBCs with deletions in CBP80 which do not affect function are described. A complex with a small N-terminal deletion in CBP80 was crystallized in space group C2 with one complex per asymmetric unit. The crystals diffract to 2 A resolution and give the first structure of intact but cap-free CBC. An additional internal deletion in CBP80 of a prominent solvent-exposed coiled coil gives rise to a more compact complex. This was co-crystallized with the cap analogue m(7)GpppG in two different crystal forms which could grow in the same drop. Form 1 belongs to space group P3(1)21 with one complex per asymmetric unit and diffracts to 2.15 A resolution. Form 2 belongs to space group P2(1)2(1)2(1) with two complexes per asymmetric unit and diffracts to 2.3 A resolution. In both forms, strong extra electron density is observed for the cap analogue and for the N- and C-terminal extensions of CBP20 which was absent or disordered in all previous structures.

Base Sequence↗
PubMed2004

Solution structure and domain architecture of the divisome protein FtsN.

Prokaryotic cell division occurs through the formation of a septum, which in Escherichia coli requires coordination of the invagination of the inner membrane, biosynthesis of peptidoglycan and constriction of the outer membrane. FtsN is an essential cell division protein and forms part of the divisome, a putative complex of proteins located in the cytoplasmic membrane. Structural analyses of FtsN by nuclear magnetic resonance (NMR) reveals an RNP-like fold at the C-terminus (comprising residues 243-319), which has significant sequence homology to a peptidoglycan-binding domain. Sequential deletion mutagenesis in combination with NMR shows that the remaining of the periplasmic region of FtsN is unfolded, with the exception of three short, only partially formed helices following the trans-membrane helix. Based on these findings we propose a model in which FtsN, anchored in the inner membrane, bridges over to the peptidoglycan layer, thereby enabling the coordination of the divisome and the murein-shaping machinery in the periplasm.

Amino Acid Sequence↗
PubMed1989

[Effects of 5-trifluoromethyl-2'-deoxyuridine (F3TdR) on ultrastructural localization of viral antigens in cultured cells infected with herpes simplex virus (HSV)].

Changes in localization of virus-associated antigens induced by F3TdR were studied using HSV-1 infected monolayer of cultured SIRC cells. A direct enzyme-antibody method was employed for preembedding for immunoelectron and light microscopy. At 3 hours post infection (h.p.i.), immunoreaction products began to appear in cytoplasm and nuclei in both the control and the F3TdR-treated group. The amounts increased during the subsequent hours of observation. In the control group, there was an intense diffuse immunoreaction in the cytoplasm and nuclei and dense accumulations of the reaction products were seen on the cell surfaces. In F3TdR-treated cells, intranuclear antigens were present as diffuse accumulations of granular deposits, and cytoplasmic stainings were very much reduced in degree; deposits on the cell surface were a rare finding. Progeny virus particles were significantly fewer in the presence of F3TdR; nucleocapsids were found but in a greatly reduced number and no enveloped particle was found. The morphology of individual nucleocapsid, however, was not significantly altered by treatment with F3TdR. A preponderance of antigenic substances in the nuclei over the cytoplasm in treatment group may reflect distorted protein synthesis and may provide morphological evidence of the biochemically assumed hypothesis of F3TdR efficacy; F3TdR exerts it's antiviral effects through abnormal protein synthesis and resultant defects in capsid assembly. Decreased antigenic substances in the membranous structures of cytoplasm may be related to reduced or abnormal production of viral antigens closely associated with envelopment.

Animals↗
PubMed1989

Transferrin receptors on the surfaces of retinal pigment epithelial cells are associated with the cytoskeleton.

Retinal pigment epithelial cells, derived from human donor eyes, have been grown in culture as monolayers on membrane filters or plastic surfaces and shown to possess transferrin receptors with a monomeric molecular mass of 93,000. These receptors internalize 125I-labelled transferrin and recycle it to the surrounding medium in a similar manner to other cell types. Scatchard analyses show that there are about 100,000 high-affinity receptors on the surface of each cell and most of these receptors are associated with the cytoskeleton. In total cell extracts, there are additional low-affinity binding sites that do not appear to be strongly associated with the cytoskeleton. The apparent interaction of transferrin receptors with the cytoskeleton was confirmed in two ways: first, using 200 kV electron microscopy for stereo analyses, skeleton-associated transferrin receptors were detected by a monoclonal anti-receptor antibody and a colloidal gold-conjugated second antibody after Triton X-100 extraction of pigment epithelial cells grown directly on laminin-coated gold grids; and, second, when cell surface receptors were labelled with radioiodinated transferrin and then incubated for various periods of time, the labelled transferrin was observed to move from a Triton X-100-insoluble fraction (a putative cytoskeletal compartment) to a Triton-soluble compartment that was not associated with the cytoskeleton. Using either horseradish peroxidase or colloidal gold-labelled transferrin, it has been shown that basolateral and apical surface-located receptors participate in receptor-mediated endocytosis via clathrin-coated pits, endosomes and tubular structures. Initially, transferrin internalized from the apical surface is observed in small endosomes that often appear to be embedded in an apical layer of microfilaments. From these peripheral regions of the cells, the labelled receptors move to larger endosomes and multivesicular bodies deeper in the cytoplasm. These structures have no apparent association with cytoskeletal elements.

Cell Division↗
PubMed1998

Function from structure? The crystal structure of human phosphatidylethanolamine-binding protein suggests a role in membrane signal transduction.

BACKGROUND: Proteins belonging to the phosphatidylethanolamine-binding protein (PEBP) family are highly conserved throughout nature and have no significant sequence homology with other proteins of known structure or function. A variety of biological roles have previously been described for members of this family, including lipid binding, roles as odorant effector molecules or opioids, interaction with the cell-signalling machinery, regulation of flowering plant stem architecture, and a function as a precursor protein of a bioactive brain neuropeptide. To date, no experimentally derived structural information has been available for this protein family. In this study we have used X-ray crystallography to determine the three-dimensional structure of human PEBP (hPEBP), in an attempt to clarify the biological role of this unique protein family. RESULTS: The crystal structures of two forms of hPEBP have been determined: one in the native state (at 2.05 A resolution) and one in complex with cacodylate (at 1.75 A resolution). The crystal structures reveal that hPEBP adopts a novel protein topology, dominated by the presence of a large central beta sheet, and is expected to represent the archaetypal fold for this family of proteins. Two potential functional sites have been identified from the structure: a putative ligand-binding site and a coupled cleavage site. hPEBP forms a dimer in the crystal with a distinctive dipole moment that may orient the oligomer for membrane binding. CONCLUSIONS: The crystal structure of hPEBP suggests that the ligand-binding site could accommodate the phosphate head groups of membrane lipids, therefore allowing the protein to adhere to the inner leaf of bilipid membranes where it would be ideally positioned to relay signals from the membrane to the cytoplasm. The structure also suggests that ligand binding may lead to coordinated release of the N-terminal region of the protein to form the hippocampal neurostimulatory peptide, which is known to be active in the development of the hippocampus. These studies are consistent with a primary biological role for hPEBP as a transducer of signals from the interior membrane surface.

Amino Acid Sequence↗
PubMed1983

Phenylalanyl-tRNA synthetases from yeast cytoplasm and mitochondria. The presence of a carbohydrate moiety in the mitochondrial enzyme and immunological evidence for structural relationship.

Homogeneous yeast cytoplasmic and mitochondrial phenylalanyl-tRNA synthetases (L-phenylalanine:tRNAPhe ligase (AMP-forming), EC 6.1.1.20) are analysed for structural differences. Only the large subunit of the mitochondrial enzyme is a glycoprotein with nearly 3% carbohydrate by weight. The carbohydrates present are: glucose, N-acetylglucosamine, mannose, galactose and N-acetylneuraminic acid. Removal of the sugar moieties yields an activity increase, but no significant change of sensitivity to proteolytic degradation. Antibodies to both homogeneous enzymes demonstrate a structural similarity for both types of subunit using the highly sensitive immunoblotting technique.

Amino Acyl-tRNA Synthetases↗
PubMed1995

The importance of intramolecular ion pairing in intermediate filaments.

Nuclear and cytoskeletal networks of 10-nm intermediate filaments (IFs) are probably ubiquitous in multicellular eukaryotes. They likely play a role in maintaining the mechanical integrity of a cell. With the exception of the nuclear lamins, IF proteins can form IFs in vitro in the absence of cofactors or associated proteins. Below we present data suggesting that the large alpha-helical "rod" domains of IF proteins are stabilized by large numbers (up to 50) of intra-helical ion pairs formed by residues of opposite charge situated four residues apart. These many ion pairs, sometimes involving up to 30% of the residues within a coiled-coil IF segment, can potentially contribute as much as 10-25 kcal/mol (1 kcal = 4.18 kJ) to the stability of a single alpha-helical rod. Such stabilization is likely to play a major role in the chemical and physical stability of IF networks in vitro and in vivo. An investigation of other coiled-coil proteins shows that selection for intrahelical ion pairing is not simply a property intrinsic to coiled-coil proteins. Rather, there is a correlation between the degree to which there is selection for intrahelical ion pairs and the extent to which a coiled-coil protein participates in highly ordered multimolecular interactions--e.g., as in IFs and myosin thick filaments. The propensity of putative ion pairs in some IF proteins--e.g., epidermal keratins--suggests that an underlying structural stability at the level of the monomer may play an important role in the extraordinary stability of dimers and higher ordered structures in cytoplasmic IFs.

Amino Acid Sequence↗
PubMed2005

Ultrastructure and localization of a visual Gq protein in hypertrophied epitoke ocelli of Perinereis brevicirris (Polychaeta, Annelida).

Functional ultrastructural changes in the rhabdomeric photoreceptors of the cerebral ocelli are described for normal and sexually mature (epitoke) Perinereis brevicirris (Polychaeta, Annelida). With sexual maturation, the cerebral ocelli hypertrophied, increasing in volume to 5.5 times that of ocelli in the normal state, and the thickness of the retinal layer increased up to 10 times. Perinereis ocelli have a pigmented retinal layer consisting of at least two cell types: photoreceptor cell (PR) and pigmented supporting cells (PS). In epitoke ocelli, PR bear well-developed rhabdomeric microvilli, multilamellar bodies, and numerous cytoplasmic membranous structures, including vesicles, smooth endoplasmic reticulum, and secondary lysosomes. Localization of a visual Gq protein in the ocelli was studied with anti-GqC antibody. The antibody strongly labeled not only microvilli and multilamellar bodies throughout the retinal layer, but also secondary lysosomes and vesicles in the cytoplasm of the PR in the epitoke ocelli, although labeling was observed only in the microvilli and multilamellar bodies in normal ocelli. Reverse transcription/polymerase chain reaction analysis revealed that the amount of G protein alpha subunit mRNA in the epitoke head increased by roughly twice that of the normal head. Since Gq protein is essential for phototransduction in Perinereis ocelli, these results suggest that the sites are involved in photoreceptive membrane turnover, which occurs much more extensively in epitoke ocelli. Thus, epitoke ocelli may represent a model system for studying rhabdomeric photoreceptive membrane turnover.

Animals↗
PubMed1995

Structure and evolution of CyI cytoplasmic actin-encoding genes in the indirect- and direct-developing sea urchins Heliocidaris tuberculata and Heliocidaris erythrogramma.

The CyI cytoplasmic actin-encoding genes of Heliocidaris erythrogramma (He), a direct-developing sea urchin, and H. tuberculata, an indirect developer, were isolated and compared to the homologous CyI gene of another indirect developer, Strongylocentrotus purpuratus. Comparisons show that despite the differences in development, the actin gene structures and sequences are highly similar. The coding and 3' untranslated regions are conserved. The 5' He regulatory region has an inserted repeat element, but is otherwise similar to its homologues in the arrangement of presumptive transcription control elements.

Actins↗
PubMed1967

An electron microscopic study of nuclear elimination from the late erythroblast.

The process of expulsion of the nucleus during the transformation of the late erythroblast to reticulocyte is described. Erythroid clones taken from the spleen of lethally irradiated mice transplanted with syngeneic bone marrow were used. 10-12-day old isolated clones were fixed in glutaraldehyde, then in osmium tetroxide. Ultra-thin sections were stained with uranyl acetate and/or lead citrate before examination. Late (orthochromatic) erythroblasts develop pseudopod-like cytoplasmic protrusions into one of which the nucleus gradually penetrates, being deformed by the extrusion through the relatively narrow passage. During the whole process, mitochondria and vesicular and membranous elements are concentrated in the cytoplasm. Once outside the cell, the nucleus reassumes its rounded form. It is surrounded by a narrow rim of cytoplasm and structurally altered plasma membrane and is connected to the rest of the cell by a bridge. Elongated vacuoles appear within this bridge, with a resulting release of the enveloped nucleus which is soon phagocytized by macrophages; this leaves behind the newly formed reticulocyte. During this process, the cytoplasmic protrusions, the agglomeration of mitochondria, and the mode of separation of the nucleus from the rest of the cell are similar to those occurring in mitotic division.

Animals↗
PubMed1983

[Effect of water-soluble antioxidants on the permeability of lysosomal membranes and on the structure of the liver in rats with thermal burns].

Experiments on rats were made to study the effect of water-soluble antioxidants on the permeability of lysosomal membranes of liver cells and liver structure under burn. Antioxidants were injected intraperitoneally shortly after burn, whereas examination was performed after one day. It has been discovered that one day after burn there takes place an appreciable destabilization of lysosomal membranes with the release of a lysosomal matrix enzyme, cathepsin D to the cytoplasm. Liver structure had undergone substantial changes by that time. After administration of water-soluble antioxidants lysosomal membranes got stabilized while liver structure manifested but insignificant disorders.

Animals↗
PubMed1999

Toxicity of 4-chloroaniline in early life stages of zebrafish (Danio rerio): II. Cytopathology and regeneration of liver and gills after prolonged exposure to waterborne 4-chloroaniline.

Ultrastructural alterations in liver and gills of embryonic and larval zebrafish (Danio rerio) following prolonged exposure to waterborne 0.05, 0.5, and 5 mg/L 4-chloroaniline for up to 31 days as well as after a 14-day regeneration period were investigated by means of light and electron microscopy. Acute toxicity was also tested at 25 and 50 mg/L. Survival of zebrafish embryos and larvae was only impaired from 25 mg/L 4-chloroaniline, but-after a transient stimulation following exposure to 0.5 mg/L-4-chloroaniline hatching was retarded after exposure to >/=5 mg/L, and fish displayed increasing rates of abnormal development and pigmentation. In contrast, hepatocytes displayed a time- and dose-dependent response from 0.05 mg/L 4-chloroaniline, including changes in nuclei, mitochondria, peroxisomes, endoplasmic reticulum, Golgi fields, lysosomes, and hepatic glycogen and lipid stores, as well as invasion of macrophages. In gills, dose-dependent effects were evident from 0.5 mg/L 4-chloroaniline and included deformation of secondary lamellae due to vacuolization and desquamation of respiratory epithelial cells in conjunction with dilation of intercellular spaces. Respiratory epithelial cells displayed progressive mitochondrial changes, induction of cytoplasmic myelinated structures, augmentation of lysosomes, and modifications of Golgi fields. Erythrocytes were severely deformed. A 14-day regeneration period was sufficient for almost complete recovery of pathological symptoms in both liver and gills. Only minor volumetric changes in hepatocellular organelles and a limited number of myelinated bodies, lysosomes, and cytoplasmic vacuoles were reminiscent of prior 4-chloroaniline exposure. In both qualitative and quantitative terms, most effects in hepatocytes after exposure of embryonic and larval zebrafish to waterborne 4-chloroaniline are comparable to the reaction of hepatocytes in adult zebrafish liver after prolonged sublethal exposure as well as in larval zebrafish after microinjection. Morphological changes in erythrocytes indicate disturbance of respiration as an additional mode of action of 4-chloroaniline.

Aniline Compounds↗
PubMed2003

Intra-epithelial neuroendocrine carcinoma of the nasal cavity.

We describe a distinctive neuroendocrine carcinoma (NEC) that proliferated intra-epithelially. The tumor was 35 mm in diameter and arose from the right superior turbinate of a 46-year-old woman. Histologically, the tumor exhibited papillary growth and the tumor cells were localized in the thickened mucosal epithelium. The tumor cells had round to oval and vesicular or hyperchromatic nuclei, and cohered without any specific structure such as a fibrillary background, rosette or glandular structure. No stromal invasion by the tumor was observed. Immunohistochemically, the tumor cells were positive for neuron-specific enolase focally. In addition, many tumor cells expressed cytokeratin (AE1/AE3 and CAM 5.2), mostly with characteristic perinuclear dot-like patterns. Electron microscopy revealed focal but well-eveloped cytoplasmic processes containing arrays of microtubules and a few dense core granules. The tumor was considered to be a poorly differentiated neuroendocrine carcinomas (NEC) that exhibited exceptional intra-epithelial proliferation. The tumor completely disappeared after the stereotactic radiosurgery and has not recurred for 40 months. It might be difficult to distinguish a poorly differentiated NEC in the sinonasal region from other neuroectodermal tumors, including olfactory neuroblastoma, but the differential diagnosis is important because each tumor has different clinicopathological characteristics.

Biomarkers, Tumor↗
PubMed1965

MEMBRANE-COATING GRANULES OF KERATINIZING EPITHELIA.

The purpose of this study has been to obtain information on the development of the envelop of horny cells that resists the action of keratinolytic agents. Toward this end the epidermis, oral mucosa, and tongue epithelium of various vertebrates, as well as the isolated envelopes of horny cells, were examined by electron microscopy. It was found that small cytoplasmic granules (1,000 to 5,000 A) that develop within differentiating epithelial cells move toward the cell periphery, and after fusion with the plasma membrane, empty their contents into the intercellular spaces. The content of the granules spreads over the cell surfaces, and subsequently a thickened and coated cell envelope is formed that resists the action of keratinolytic agent. The membrane-coating granule is regarded as a specific differentiation product of the keratinizing epithelium. It contains numerous inner membranes and is assumed to engage in synthetic activities such as, perhaps, the formation of polysaccharides.

Animals↗