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PubMed1995

Geometrical analysis of structural changes in immunoglobulin domains' transition from native to molten state.

Molecular dynamics simulation (300, 320, 340 K) performed on the Fab (Kol) fragment of immunoglobulin G revealed that the structural changes associated with relaxation of peptides after their release from the stabilized by the tertiary interaction native conformation may be considered characteristic of the transition from native to molten state. The configuration of peptide chains at temperatures close to melting, liberated from the constraints associated with tertiary packing, was found to deviate toward helical rather than extended forms. The direction of the shift is diagonal on the phi-psi map. The torsional angles tend to concentrate in the Cea7 region, and some leak to the alphaR area. The geometrical parameters designed to describe the configuration of the peptide chain in Fab fragment also confirmed that during melting the peptides generally moved toward helical form.

Crystallography, X-Ray↗
PubMedDate not supplied

Different structural changes in membrana Shrapnelli in serous and purulent otitis media. An experimental study in the rat.

In an animal model, production of serous and purulent effusion material was induced by blocking the Eustachian tube and cleaving the soft palate, respectively. Two and 6 weeks after the different surgical procedures, animals were sacrificed and the membrana Shrapnelli was analysed by light- and electronmicroscopy. The two types of middle ear effusion were associated with various structural changes of the membrana Shrapnelli. In serous otitis media the pars flaccida appeared fibrotic, with large dilated vessels. Sometimes its inner layer, facing the attic space, was contiguous with the investing layer of the ossicles. In purulent otitis media the pars flaccida was thickened and the inner epithelial lining was replaced by a pseudostratified squamous epithelium containing ciliated and secretory cells. Ciliated cells lining the pars flaccida appeared pathognomonic for a longstanding middle ear infection. It is inferred that the structure of membrana Shrapnelli changes under the influence of inflammatory conditions in the middle ear cavity, changes which specifically reflect the different types of otitis media.

Animals↗
PubMed1994

Structural changes in the endoplasmic reticulum of starfish oocytes during meiotic maturation and fertilization.

The endoplasmic reticulum (ER) of live starfish oocytes was observed during meiotic maturation and fertilization. The ER was visualized by injection into the cytoplasm of an oil drop saturated with the fluorescent lipophilic dye DiI; DiI spread throughout the oocyte endoplasmic reticulum and the pattern was imaged by confocal microscopy. The ER in the immature (germinal vesicle stage) oocyte was composed of interconnected membrane sheets. In response to 1-methyladenine, the sheets of ER appeared to become associated with the yolk platelets, forming spherical shells. A few of these spherical shells could sometimes be seen in immature oocytes, but their number was much greater in the egg at the first meiotic spindle stage. At about the time that the first polar body formed, the spherical shells disappeared, and the ER returned to a form like that of the immature oocyte. The spherical shells did not reappear during the second meiotic cycle. During maturation, the ER also began to move; the movement was apparent by the time of germinal vesicle breakdown and continued throughout both meiotic cycles and in eggs with second polar bodies. When eggs at the first meiotic spindle stage were fertilized, the form of the ER changed. Within 1 min after sperm addition to the observation chamber, the circular cross sections of the spherical shells of the unfertilized egg ER were no longer distinct. At this point, the form of the ER could not be discerned with the resolution of the light microscope; however, the rate of spreading of DiI from an injected oil drop decreased, providing strong evidence that the ER had become fragmented. The ER remained in this form for several minutes and then gradually, the appearance of the ER and the rate of DiI spreading returned to be like those of the unfertilized egg. Injection of inositol trisphosphate caused a similar change in the ER structure. These results indicate that the ER is a dynamic structure, the form of which changes during oocyte maturation and fertilization.

Animals↗
PubMed1994

Energy-induced structural changes in NADH:Q oxidoreductase of the mitochondrial respiratory chain.

The reaction of coupled submitochondrial particles (SMP) with NADH was studied in the absence and presence of the uncoupler gramicidin, both in pre-steady-state and steady-state experiments. It was shown that the formation of ubisemiquinones associated with NADH:Q oxidoreductase is insensitive to uncouplers. It was found, however, that in the absence of gramicidin the ubisemiquinone showed a noticeably faster relaxation than in the presence of this uncoupler. During steady-state oxidation of NADH by coupled submitochondrial particles, the EPR signal of iron-sulphur cluster 2 of complex I, the cluster that is generally believed to be the electron donor for ubiquinone, showed some remarkable changes. Its gz line seemed to disappear from the spectrum, although the gxy line remained clearly present. Detailed EPR analysis indicated that (a component of) the gz line shifted to higher field. The temperature dependence of the EPR signal of cluster 2 was affected as well. In the presence of uncoupler the EPR properties of cluster 2 were indistinguishable from those in particles that showed no intrinsic coupling. These experiments strongly indicate that the coordination of cluster 2 is different in energized and non-energized SMP. The pre-steady-state reaction between these submitochondrial particles and NADH showed that the uncoupler-sensitive changes in both the ubisemiquinone and cluster 2 became effective between 9 ms and 30 ms. Similar changes were observed during succinate-driven reverse electron transfer. This report shows, for the first time, energy-induced structural changes in NADH:Q oxidoreductase.

Electron Spin Resonance Spectroscopy↗
PubMed1977

Structural changes on Entamoeba histolytica trophozoites after cryopreservation in liquid nitrogen.

Trophozoites of Entamoeba histolytica cultures which had been deep-frozen in the presence of 5% DMSO, along with untreated cells and cells treated with DMSO (5%), were examined for fine-structural changes. After deep-freezing in liquid nitrogen only a few amoebae exhibited normal nuclear and cytoplasmic structure. One frequently observed but unspecific finding pertaining to recovered cells is the separation of the cytoplasm into large vacuolated (coarse-granular) and electron-optically fine-granular (hyaline) zones. The glycogen which normally lies in the cytoplasm is always eluted. In many cases numerous short RNP helices are scattered unevenly in the vesicular plasma, but they are also found in larger masses adjacent to the membranes of still intact and already damaged nuclei. Moderately damaged nuclei have a poorly folded membrane and their chromatin is markedly denatured. More heavily damaged nuclei have a membrane which has partly fibrillated or ruptured and then formed conspicuous folds, where the nuclear membrane has ruptured nucleoplasmic remnants of chromatin and button-like bodies appear to pour into the surrounding cytoplasm. The final destruction of the cell is marked by coalescing autolytic zones, first in the vacuolated and later in the fine-granular cytoplasm. Finally only remnants of the nuclear membrane and of the membranes of numerous vacuoles remain. It is assumed that most of the changes in the cytoplasm are of a secondary nature and are caused by the early functional disturbance of the nucleus.

Animals↗
PubMed1986

Proximal tubular atrophy: qualitative and quantitative structural changes in chronic obstructive nephropathy in the pig.

Kidneys of pigs with various degrees of induced chronic obstructive nephropathy were studied by light- and electron microscopy to assess the structural changes of proximal convoluted tubules with increasing degrees of atrophy. A particular aim was to evaluate the quantitative relationship between proximal tubular and interstitial changes in early tubular atrophy. The kidneys were subjected to varying degrees of ureteral obstruction and were fixed by in vivo vascular perfusion. Quantitative (morphometric) analyses were carried out on montages of electron micrographs representing randomly selected cortical areas and cross sections of individual proximal convoluted tubules. The results demonstrated that ureteral obstruction was followed by significant reductions in proximal tubular epithelium, in volume of proximal tubular mitochondria and in surface area of proximal tubular basolateral membranes. These changes were present even in the absence of any demonstrable increase in cortical interstitium or alterations in the relationships between proximal tubules and peritubular capillaries. With increase in the volume of cortical interstitium the proximal tubules were further simplified in ultrastructure with a reduced number of interdigitating lateral cell processes. Concomitantly there were significant quantitative changes in the spatial associations between tubules and capillaries due to increase in tubulo-capillary distances. The present study shows that ultrastructural changes in proximal tubules during early atrophy precede the volume increase in cortical interstitium associated with chronic obstructive nephropathy. It is suggested that the early tubular changes are due to decreased functional loads, whereas the further progression of tubular atrophy may be a result of impaired nourishment of the tubular cells due to increased interstitial tissue and altered relationships between tubules and capillaries.

Animals↗
PubMed2005

Structural changes induced by lattice-electron interactions: SiO2 stishovite and FeTiO3 ilmenite.

The bright source and highly collimated beam of synchrotron radiation offers many advantages for single-crystal structure analysis under non-ambient conditions. The structure changes induced by the lattice-electron interaction under high pressure have been investigated using a diamond anvil pressure cell. The pressure dependence of electron density distributions around atoms is elucidated by a single-crystal diffraction study using deformation electron density analysis and the maximum entropy method. In order to understand the bonding electrons under pressure, diffraction intensity measurements of FeTiO3 ilmenite and gamma-SiO2 stishovite single crystals at high pressures were made using synchrotron radiation. Both diffraction studies describe the electron density distribution including bonding electrons and provide the effective charge of the cations. In both cases the valence electrons are more localized around the cations with increasing pressure. This is consistent with molecular orbital calculations, proving that the bonding electron density becomes smaller with pressure. The thermal displacement parameters of both samples are reduced with increasing pressure.

Journal Article↗
PubMed2006

Elevated CO2 induces physiological, biochemical and structural changes in leaves of Arabidopsis thaliana.

Leaves of Arabidopsis thaliana grown under elevated or ambient CO2 (700 or 370 micromol mol(-1), respectively) were examined for physiological, biochemical and structural changes. Stomatal characters, carbohydrate and mineral nutrient concentrations, leaf ultrastructure and plant hormone content were investigated using atomic absorption spectrophotometry, transmission electron microscopy and enzyme-linked immunosorbent assay (ELISA). Elevated CO2 reduced the stomatal density and stomatal index of leaves, and also reduced stomatal conductance and transpiration rate. Elevated CO2 increased chloroplast number, width and profile area, and starch grain size and number, but reduced the number of grana thylakoid membranes. Under elevated CO2, the concentrations of carbohydrates and plant hormones, with the exception of abscisic acid, increased whereas mineral nutrient concentrations declined. These results suggest that the changes in chloroplast ultrastructure may primarily be a consequence of increased starch accumulation. Accelerated A. thaliana growth and development in elevated CO2 could in part be attributed to increased foliar concentrations of plant hormones. The reductions in mineral nutrient concentrations may be a result of dilution by increased concentrations of carbohydrates and also of decreases in stomatal conductance and transpiration rate.

Arabidopsis↗
PubMed2001

Thymic structural changes in relation to seasonal cycle and testosterone administration in wall lizard Hemidactylus flaviviridis (Ruppell).

Light microscopic and ultrastructural studies of thymus in wall lizard showed remarkable season dependent structural changes. In winter, the thymus was involuted and its cortico-medullary differentiation was not distinct. Thymocytes were sparsely distributed. The epithelial cells exhibited atrophic features such as an appreciable decrease in the nuclear-cytoplasmic ratio and accordingly reduction in cell organelles. The reconstruction of thymus commenced during spring and it became fully developed with marked delineation of cortico-medullary regions during summer. The thymus was then densely populated with thymocytes and epithelial cells showed voluminous cytoplasm having numerous cell organelles. The thymus regression started again by the beginning of autumn. The results suggest that the thymic development in wall lizard have inverse relationship with the androgen level, as the testicular steroidogenic activity was seen maximum during winter and least in summer. This assumption gets support by castration and testosterone replacement experiments. Castration of lizards during winter resulted in profound development of thymus with an appreciable increase in thymocytes mainly in the cortex region . The cortex became delineated from the medulla. Following testosterone treatment, the thymus underwent regression and was comparable to testis-intact lizard's thymus during winter season. After withdrawal of testosterone treatment, the thymus exhibited dense lymphoid and thymocyte population with a demarcation of cortico-medullary regions and sub-cortical region was regenerated.

Androgens↗
PubMed1980

Studies on structural changes of F-actin and myosin in living, intact and damaged muscle fibres by means of polarized ultraviolet fluorescence microscopy.

By means of polarized ultraviolet fluorescence microscopy the structural changes of F-actin and myosin were discovered at the changing a functional state of a living muscle fibre and during spreading degeneration (Zenker's necrosis). The character of conformational changes of F-actin and myosin at activation, contraction, contracture and rigor is similar, but the number of changed macromolecules depends on a fibre state. At fibre local damage in its morphological intact parts there was found an alternation of zones, reflecting two states unusual for a fibre. During spreading degeneration these states transform into irreversible contracture and then into rigor. Similar changes were observed in muscle fibres obtained from denervated muscles.

Actins↗
PubMed1991

Direct sequencing of the dopamine D2 receptor (DRD2) in schizophrenics reveals three polymorphisms but no structural change in the receptor.

The dopamine D2 receptor gene (gene symbol DRD2) is a candidate gene for schizophrenia because the potency of certain neuroleptics correlates with their affinity for this receptor. Seven regions of likely functional significance including the coding sequences and the splice junctions were fully sequenced in the dopamine D2 receptor of 14 schizophrenics (and partially in several others) meeting DSM-III-R diagnostic criteria and in four unaffected non-Caucasians (97 kb of total sequence). No structural changes were found, suggesting that alteration in the structure of the dopamine D2 receptor is not commonly involved in the etiology of schizophrenia. However, two common and one uncommon intragenic polymorphisms were found. At least one of the polymorphisms was informative for linkage in 70% of Caucasians and 78% of Koreans.

Base Sequence↗
PubMed2002

Human glutathione-dependent formaldehyde dehydrogenase. Structural changes associated with ternary complex formation.

Human glutathione-dependent formaldehyde dehydrogenase plays an important role in the metabolism of glutathione adducts such as S-(hydroxymethyl)glutathione and S-nitrosoglutathione. The role of specific active site residues in binding these physiologically important substrates and the structural changes during the catalytic cycle of glutathione-dependent formaldehyde dehydrogenase was examined by determining the crystal structure of a ternary complex with S-(hydroxymethyl)glutathione and the reduced coenzyme to 2.6 A resolution. The formation of the ternary complex caused the movement of the catalytic domain toward the coenzyme-binding domain. This represents the first observation of domain closure in glutathione-dependent formaldehyde dehydrogenase in response to substrate binding. A water molecule adjacent to the 2'-ribose hydroxyl of NADH suggests that the alcohol proton is relayed to solvent directly from the coenzyme, rather than through the action of the terminal histidine residue as observed in the proton relay system for class I alcohol dehydrogenases. S-(Hydroxymethyl)glutathione is directly coordinated to the active site zinc and forms interactions with the highly conserved residues Arg114, Asp55, Glu57, and Thr46. The active site zinc has a tetrahedral coordination environment with Cys44, His66, and Cys173 as the three protein ligands in addition to S-(hydroxymethyl)glutathione. This is in contrast to zinc coordination in the binary coenzyme complex where all of the ligands were contributed by the enzyme and included Glu67 as the fourth protein ligand. This change in zinc coordination is accomplished by an approximately 2.3 A movement of the catalytic zinc.

Aldehyde Oxidoreductases↗
PubMed1996

Kupffer cell inactivation prevents lipopolysaccharide-induced structural changes in the rat liver sinusoid: an electron-microscopic study.

Scanning and transmission electron-microscopic examination of the rat liver sinusoid was performed in this study after in vivo treatment of rats with gram-negative bacterial lipopolysaccharide (LPS, 1 mg/Kg(-1) body weight), with or without pretreatment with gadolinium chloride (GdCl3 10 mg(Kg(-1) body weight). Twenty-seven and 48 hours after GdCl3 administration, to inactivate/eliminate part of the Kupffer cell population, a decrease in the number of visualized Kupffer cells was observed, without evident effects on the sinusoidal endothelial cell or on the hepatocyte. Three and 24 hours after its administration, LPS produced ultrastructural changes in the sinusoid characterized by morphological evidence of Kupffer cell activation (i.e., swelling and expanded philopodia anchoring the Kupffer cell to the luminal surface of the sinusoidal wall), and a marked decrease in the population of endothelial cell fenestration. The reduction in the number of fenestrae was associated with a change in the diameter of fenestrae and can be interpreted as a component of the "capillarization" process of the hepatic sinusoid. Such ultrastructural changes were prevented by the administration of GdCl3 24 hours before LPS injection. Hence, these findings suggest that LPS-induced structural changes in the liver sinusoid are mediated by an LPS-induced Kupffer cell activation. Coupled with previous experimental data, showing similar effects of GdCl3 on one of the hepatic sinusoidal endothelial cell (SEC) functions, i.e., hyaluronan scavenging, the data presented in this study strongly support the view that Kupffer cells modulate both the hepatic SEC's functional as well as ultrastructural properties.

Animals↗
PubMed2006

Chronic spinal nerve ligation induces microvascular permeability disturbances, astrocytic reaction, and structural changes in the rat spinal cord.

The possibility that a chronic nerve ligation impairs the spinal cord cellular microenvironment was examined using leakage of endogenous albumin, reaction of astrocytes, and structural changes in a rat model. Rats subjected to 8 weeks of unilateral L4/L5 nerve ligation (a model of neuropathic pain) showed leakage of albumin, up-regulation of glial fibrillary acidic protein (GFAP) immunoreaction, and abnormal cell reaction. Distortion and loss of nerve cells as well as general sponginess of the gray matter was clearly evident. Cell changes were present in both dorsal and ventral horns and were most marked on the ipsilateral side compared to the contralateral cord. Nerve cell and glial cell changes are normally present in the regions showing intense albumin immunoreactivity, indicating disruption of the blood-spinal cord barrier (BSCB). Our observations indicate that a chronic nerve lesion has the capacity to induce selective breakdown of the BSCB that could be responsible for activation of astrocytes and abnormal cell reaction. These findings enhance our understanding of the pathophysiology of neuropathic pain and/or other spinal cord disorders.

Adaptation, Physiological↗
PubMed2005

Structural changes to electronic gaming machines as effective harm minimization strategies for non-problem and problem gamblers.

This study aimed to evaluate the effectiveness of three proposed modifications to the structural characteristics of electronic gaming machines as harm minimisation strategies for non-problem and probable problem gamblers. Structural changes included reducing the maximum bet size, reducing reel spin and removing large note acceptors. Behavioural patterns of play were observed in 779 participants attending clubs and hotels. Observations were conducted in the gaming venue during regular gaming sessions. Eight experimental machines were designed to represent every combination of the modifications. 210 participants played at least one modified and one unmodified machine. Following play, the South Oaks Gambling Screen (SOGS) was administered. More problem than non-problem gamblers used high denomination bill acceptors and bet over one-dollar per wager. Machines modified to accept the one-dollar maximum bet were played for less time and were associated with smaller losses, fewer individual wagers and lower levels of alcohol consumption and smoking. It was concluded that the reduction of maximum bet levels was the only modification likely to be effective as a harm minimization strategy for problem gamblers.

Adult↗
PubMed1997

Transthyretin quaternary and tertiary structural changes facilitate misassembly into amyloid.

Human transthyretin (TTR) can be transformed into amyloid fibrils by partial acid denaturation to yield a monomeric amyloidogenic intermediate that self-associates into amyloid through quaternary structural intermediates, which are identified by sedimentation velocity methods. The monomeric amyloidogenic intermediate has substantial beta-sheet structure with a nonnative but intact tertiary structure as discerned from spectroscopic methods. Proteolysis sensitivity studies suggest that the C-strand-loop-D-strand portion of TTR becomes disordered and moves away from the core of the beta-sandwich fold upon formation of the monomeric amyloidogenic intermediate over the pH range 5.1-3.9. The single site mutations that are associated with early onset amyloid disease [familial amyloid polyneuropathy (FAP)] function by destabilizing tetrameric TTR. Under mild denaturing conditions, the FAP variants populate the monomeric amyloidogenic intermediate conformation, which assembles into amyloid, whereas wild-type TTR remains tetrameric and nonamyloidogenic. The FAP mutations do not significantly alter the native folded structure; instead, they appear to act by making the thermodynamics and perhaps the kinetics more favorable for formation of the amyloidogenic intermediate. Suppressor mutations have also been characterized that strongly stabilize tetrameric TTR and disfavor the formation of the monomeric amyloidogenic intermediate, thus inhibiting amyloid formation. The mechanistic details characterizing transthyretin amyloid fibril formation available from the biophysical studies outlined within have been utilized to develop a new therapeutic strategy for intervention in human amyloid disease. This approach features small molecules that bind with high affinity to the normal fold of transthyretin, inhibiting the quaternary and tertiary structural changes associated with the formation of the monomeric amyloidogenic intermediate that self-assembles into amyloid. Ligand binding to TTR stabilizes the native tetrameric fold, which is nonamyloidogenic.

Amyloid↗