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PubMed1984

Diabetes-associated endometrial disruption in the Chinese hamster: structural changes in relation to progressive hyperglycemia.

The relationship between progressive diabetes and endometrial structure was examined in genetically diabetic Chinese hamsters. Uterine samples were collected from animals exhibiting prediabetic to overt diabetic conditions and from matched control animals. In controls (with blood glucose levels less than or equal to 145 mg/dl) the endometrium was typified by an intact luminal epithelium, a thin underlying basement membrane and a well-organized stroma layer. In contrast, mildly diabetic (150-250 mg/dl) animals exhibited a compressed luminal epithelium which was embedded in a thickened basement membrane infiltrated with phagocytic blood elements. The stromal layer contained several irregular cells which were characterized by cytoplasmic vacuolization and collagen fiber separation by an amyloid-like, intercellular ground substance. In overt diabetic animals (greater than or equal to 300-500 mg/dl), the luminal epithelial cells were located over a greatly thickened basement membranes which was infiltrated by phagocytic blood elements and degenerating stromal cell membranes. The lumens of the glands were closed and the stromal cells were separated by an increased intercellular space occupied by an amyloid-like ground substance. Many stromal cells exhibited cytoplasmic vacuolization. These studies demonstrate that uterine involution associated with diabetes occurs in a sequential manner and is temporally related to progressive elevations in blood glucose levels.

Animals↗

PubMed1991

[Structural changes in valve prostheses].

All available prostheses, either mechanical or biological, may undergo structural alterations which are cause of reoperation or death. Some of these complications are common to all valves, whereas some are specific for certain models. Modern mechanical prostheses usually are resistant to structural deterioration, but still thrombogenic thus requiring long-term anticoagulation therapy to avoid thrombotic and thromboembolic episodes, which implies the risk of anticoagulation related hemorrhages. Bioprostheses, on the other hand, present a lower thrombogenicity, however they undergo by definition structural degeneration, especially dystrophic calcification, which is usually cause of reoperation within 8-10 years from implantation. Other prosthetic complications, such as infective endocarditis and fibrous tissue overgrowth, are common to both types of prostheses.

Bioprosthesis↗

PubMed2004

Inhibitor-induced structural change of the active site of human poly(ADP-ribose) polymerase.

The crystal structure of human recombinant poly(ADP-ribose) polymerase (PARP) complexed with a potent inhibitor, FR257517, was solved at 3.0 A resolution. The fluorophenyl part of the inhibitor induces an amazing conformational change in the active site of PARP by motion of the side chain of the amino acid, Arg878, which forms the bottom of the active site. Consequently, a corn-shaped hydrophobic subsite, which consists of the side chains of Leu769, Ile879, Pro881, and the methylene chain of Arg878, newly emerges from the well-known active site.

Binding Sites↗

PubMed1976

[Effect of quercitrin on structural changes in the large and small intestines in experimental enterocolitis].

Sensitization of rats with the homologous antigen of the large intestine with Freund's stimulant caused marked immunomorphological shift in the large intestine of rats with the phenomena of enteritis in the small intestine. Oral administration of quercitrin in doses of 25 and 100mg/kg for 10 days promoted decline of focal lymphohistiomonocytic infiltrations, of eosinophilic in the mucosa and of scleroti changes in the large intestine. At the same time restoration of structural disturbances occurred in the small intestine. The influence of quercitrin on the morphological changes in the epithelium of the large and small intestine mucosa were insignificant. It is believed that the therapeutic action of quercitrin could be caused by restoration of local circulation deranged in animal sensitization.

Animals↗

PubMed2000

[Structural changes in vestibular nuclei of macaca mulatta brain following flight in satellite Bion-11].

The structure of vestibular nuclei cells was studied in the brain of Macaca mulatta on return from the 14-d flight on satellite BION-11 and in 2 days of recovery. The monkey suddenly deceased on day 2 since landing because of aspiration asphyxia on completion of biopsy of muscle and bone tissues. Basic shifts in neural cells of the vestibular nuclei were focal tigrolysis and formation of larger clodlets by remains of tigroid. The most pronounced changes occurred to cells in the medial, upper and descending vestibular nuclei. Deiter's lateral vestibular nucleus was least changed. The conclusion has been made that loss of reactivity by vestibular nuclei in microgravity is linked not only with the effects of exterofactors (otolith and labyrinthine receptors) but also with the structural-functional deficiency of cells of vestibular nuclei.

Animals↗

PubMedDate not supplied

[Role of the structural changes of lungs in thanatogenesis of cranio-cerebral complicated trauma].

The lungs of 27 persons, who died of severe craniocerebral and combined trauma, were histologically examined. A deformation of the bronchi is registered in 15-60 min after craniocerebral trauma; desquamated epithelium and mucinous contents are found in their lumens. Erythrocytes and macrophages are detected in the alveolar lumens. The capillary alveolar septums are full-blooded; the alveolar septums are edematous with signs of hemorrhages and clusters of lymphoid cells. The venules are enlarged and full-blooded. Regions of the emphysema alternate with dystelectases and atelectases. The interstitial edema set on and the alveolar edema aggravates in 2-8 hours after trauma. There is an aggregation of erythrocytes. The leukocytic infiltration worsens. Hyaline membranes take shape. Similar changes are observed in the lungs in case of combined trauma; at the same time, the morphological changes are faster in the latter trauma variation. The detected structural impairments are typical of an acute pulmonary lesion and are crucial in thanatogenesis in craniocerebral and combined trauma.

Adult↗

PubMed2006

Desiccation tolerance in the moss Polytrichum formosum: physiological and fine-structural changes during desiccation and recovery.

BACKGROUND AND AIMS: This study explores basic physiological features and time relations of recovery of photosynthetic activity and CO(2) uptake following rehydration of a desiccation-tolerant moss in relation to the full temporal sequence of cytological changes associated with recovery to the normal hydrated state. It seeks reconciliation of the apparently conflicting published physiological and cytological evidence on recovery from desiccation in bryophytes. METHODS: Observations were made of water-stress responses and recovery using infrared gas analysis and modulated chlorophyll fluorescence, and of structural and ultrastructural changes by light and transmission electron microscopy. KEY RESULTS: Net CO(2) uptake fell to zero at approx. 40 % RWC, paralleling the fluorescence parameter PhiPSII at 200 micromol m(-2) s(-1) PPFD. On re-wetting the moss after 9-18 d desiccation, the initially negative net CO(2) uptake became positive 10-30 min after re-wetting, restoring a net carbon balance after approx. 0.3-1 h. The parameter F(v)/F(m) reached approx. 80 % of its pre-desiccation value within approx. 10 min of re-wetting. In the presence of the protein-synthesis inhibitors chloramphenicol and cycloheximide, recovery of F(v)/F(m) (and CO(2) exchange) proceeded normally in the dark, but declined rapidly in the light. Though initial recovery was rapid, both net CO(2) uptake and F(v)/F(m) required approx. 24 h to recover completely to pre-desiccation values. The fixation protocols produced neither swelling of tissues nor plasmolysis. Thylakoids, grana and mitochondrial cristae remained intact throughout the drying-re-wetting cycle, but there were striking changes in the form of the organelles, especially the chloroplasts, which had prominent lobes and lamellar extensions in the normally hydrated state, but rounded off when desiccated, returning slowly to their normal state within approx. 24 h of re-wetting. Sub-cellular events during desiccation and re-wetting were generally similar to those seen in published data from the pteridophyte Selaginella lepidophylla. CONCLUSIONS: Initial recovery of respiration and photosynthesis (as of protein synthesis) is very rapid, and independent of protein synthesis, suggesting physical reactivation of systems conserved intact through desiccation and rehydration, but full recovery takes approx. 24 h. This is consistent with the cytological evidence, which shows the thylakoids and cristae remaining intact through the whole course of dehydration and rehydration. Substantial and co-ordinated changes in other cell components, which must affect spatial relationships of organelles and metabolic systems, return to normal on a time span similar to full recovery of photosynthesis. Comparison of the present data with recently published results suggests a significant role for the cytoskeleton in desiccation responses.

Adaptation, Physiological↗

PubMed1987

Synaptic structural changes during development and aging.

Although a great deal is known about the development of synaptic number, comparatively little is known about the effects of development, and particularly aging, on the structure of the synapse. The present study examined synaptic structure in the molecular layer of the motor-sensory neocortex during early development (postnatal days (P) 1, 3, 5, 7, 10, 15, 20, 30), adulthood (P60, 90), and old age (28 months). Tissue was stained with osmium tetroxide (osmium) or ethanol phosphotungstic acid and the following synaptic characteristics were quantified: (1) presynaptic element length, area, thickness, maximal projection height and smoothness, and number and size of vesicles adjacent to the presynaptic element; (2) postsynaptic element length, area, and thickness; and (3) cleft width. There is an early developmental increase in synaptic element length, followed by an increase in thickness into adulthood. During development the height and width of the presynaptic dense projections increase, after which they remain stable. While the number of adjacent synaptic vesicles increases throughout the lifespan, there is a parallel decrease in their size. During the period of rapid synaptogenesis in this brain region there are no decreases in any of the synaptic structural parameters examined, indicating that newly generated synapses are either formed the same size as the existing mature synapses, or are extremely plastic and grow very rapidly. Unlike age-associated changes in synaptic number, no changes were found in synaptic structure during aging.

Aging↗

PubMed2004

Structure and structural changes of the silk fibroin from Samia cynthia ricini using nuclear magnetic resonance spectroscopy.

The structure of silk fibroin from a wild silkworm, S. c. ricini, the amino acid sequence of which consists of repeated poly-Ala and Gly-rich regions, was examined by using solution and solid-state NMR methods. The structural transition of the silk fibroin in aqueous solution was monitored by using 13C solution NMR spectroscopy as a function of temperature. The fast exchange with respect to the chemical shift between the helix and coil conformations was observed in the poly-Ala region and the slow conformational change from alpha-helix to random coil was observed for the Gly residue adjacent to the N-terminal Ala residue of the poly-Ala region. The torsion angles of several Ala and Gly residues in the model peptide, GGAGGGYGGDGG(A)12GGA-GDGYGAG, were determined by the conformation-dependent 13C chemical shifts, rotational echo double resonance (REDOR) and 2D spin-diffusion NMR methods. The solid-state NMR analysis leads to the precise silk structure before spinning, where the poly-Ala sequence takes a typical alpha-helix pattern with a tightly winded helical structure at both terminal regions of the poly-Ala sequence. This is expected to stabilize the alpha-helical structure of the poly-Ala region in S. c. ricini silk fibroin from the silkworm.

Amino Acids↗

PubMed2005

Structural changes of the complex between pharaonis phoborhodopsin and its cognate transducer upon formation of the M photointermediate.

pharaonis phoborhodopsin (ppR, also called pharaonis sensory rhodopsin II, psRII) is a receptor for negative phototaxis in Natronobacterium pharaonis. It forms a 2:2 complex with its transducer protein, pHtrII, in membranes, and the association is weakened by 2 orders of magnitude in the M intermediate. Such change is believed to correspond to the transfer of the light signal to pHtrII. In this paper, we applied Fourier transform infrared (FTIR) spectroscopy to the active M intermediate in the absence and presence of pHtrII. The obtained difference FTIR spectra were surprisingly similar, notwithstanding the presence of pHtrII. This result strongly suggests that the transducer activation in the ppR-pHtrII system does not induce secondary structure alterations of the pHtrII itself. On the other hand, we found that the hydrogen bond of the OH group of Thr204 is altered in the primary K intermediate, but restored in the M intermediate. The hydrogen bond of Asn74 in pHtrII is strengthened in M, presumably because of the change in interaction with Tyr199 of ppR. These facts provided a light signaling pathway from Lys205 (retinal) of the receptor to Asn74 of the transducer through Thr204 and Tyr199. Transducer activation is likely to involve a relaxation of Thr204 in the receptor and hydrogen bonding alteration of Asn74 in the transducer, during which the helices of the transducer perform rigid-body motion without changing their secondary structures.

Archaeal Proteins↗

PubMed2001

Distinct structural changes detected by X-ray fiber diffraction in stabilization of F-actin by lowering pH and increasing ionic strength.

Lowering pH or raising salt concentration stabilizes the F-actin structure by increasing the free energy change associated with its polymerization. To understand the F-actin stabilization mechanism, we studied the effect of pH, salt concentration, and cation species on the F-actin structure. X-ray fiber diffraction patterns recorded from highly ordered F-actin sols at high density enabled us to detect minute changes of diffraction intensities and to precisely determine the helical parameters. F-actin in a solution containing 30 mM NaCl at pH 8 was taken as the control. F-actin at pH 8, 30 to 90 mM NaCl or 30 mM KCl showed a helical symmetry of 2.161 subunits per turn of the 1-start helix (12.968 subunits/6 turns). Lowering pH from 8 to 6 or replacing NaCl by LiCl altered the helical symmetry to 2.159 subunits per turn (12.952/6). The diffraction intensity associated with the 27-A meridional layer-line increased as the pH decreased but decreased as the NaCl concentration increased. None of the solvent conditions tested gave rise to significant changes in the pitch of the left-handed 1-start helix (approximately 59.8 A). The present results indicate that the two factors that stabilize F-actin, relatively low pH and high salt concentration, have distinct effects on the F-actin structure. Possible mechanisms will be discussed to understand how F-actin is stabilized under these conditions.

Actins↗

PubMed1976

4-Thiouridine, a built-in probe for structural changes in transfer RNA.

The luminescence of an aqueous solution of 4-thiouridine was compared with its emission when forming part of the polynucleotide chain of tRNA. In both cases excitation into the last absorption band at 335 nm yields a weak emission in the 520--550 nm region. However, while in aqueous solution this emission has a lifetime of approximately 240 ns, it increases in native tRNA to tau congruent to 6.6 mus. Oxygen and Cl- ions quench the thiouridine emission efficiently in aqueous solution while Na+ and Mg2+ ions have no influence on it. On the other hand thiouridine which forms part of a tRNA molecule is quite insensitive to Cl- ions and to O2 while its emission is greatly enhanced by Na+ and Mg2+ ions. From these salt effects as well as from data on the temperature dependence of the emission yield and the decay curve, it is concluded that the site of the thiouridine residue is very well protected within the tertiary structure of tRNA. Both permanent changes in the secondary and in the tertiary structures of the polynucleotide as well as dynamic conformation changes can be observed by following the emission characteristics of its thiouridine residue.

Binding Sites↗

PubMed1992

Closed circular DNA as a probe for protein-induced structural changes.

Biological systems are replete with examples of DNA formed into a closed loop structure, either alone or in close association with proteins. Such closed circular DNA molecules are subject to a topological constraint that modifies, often in a major way, the structure and reactivity of the DNA. The topological constraint also permits closed circular DNAs to be used as analytical tools to learn about the structure of DNA-protein complexes.

DNA Probes↗

PubMed2003

Atomic force microscopy study of chromosome surface structure changed by protein extraction.

We applied atomic force microscopy (AFM) to investigate the surface structure of barley chromosome in combination with a chemical treatment method. As a result, we have obtained high-resolution topographic images of granular structures with a diameter of ca. 50 nm on the surface of critical-point dried metaphase chromosomes. Treatment with 2M NaCl significantly modified the chromosome surface structure: surface roughness was increased and chromosome thickness was decreased. The NaCl treatment extracted two major proteins with molecular weights of 4000 and 20,000 Da. These proteins might be belonging to non-histone protein families that do not contain any aromatic amino acid. The results demonstrate the advantage of the combined method of high-resolution AFM imaging and chemical treatments for understanding nano-scale surface structures of the chromosome.

Chromosome Structures↗

PubMed1989

Long-range structural changes in proteinase K triggered by calcium ion removal.

The X-ray crystal structure of the subtilisin-type enzyme proteinase K at 1.5 A resolution shows that is has two binding sites for Ca2+. Scatchard analysis indicates that one Ca2+ binds tightly, with pK 7.6 x 10(-8) M-1, and the other only weakly. Although Ca2+ is not directly involved in the catalytic mechanism and is 16.6 A away from the alpha-carbon atoms of the catalytic triad Asp 39-His 69-Ser 224, the activity of proteinase K towards the synthetic substrate succinyl-Ala-Ala-Ala-p-nitroanilide drops slowly to approximately 20% of its original value when it is depleted of Ca2+. This is not due to autolysis of the enzyme. The X-ray crystal structure of Ca2+-free proteinase K shows that removal of Ca2+ from the tight binding site triggers a concerted domino-like movement of five peripheral loops and of two alpha-helices. At a distance of 25 A from this calcium-binding site, the geometry of both the secondary substrate binding site and of the catalytic triad is affected by this movement thereby reducing the activity of the enzyme.

Binding Sites↗

PubMed1992

Structural changes and lateral redistribution of photosystem II during donor side photoinhibition of thylakoids.

The structural and topological stability of thylakoid components under photoinhibitory conditions (4,500 microE.m-2.s-1 white light) was studied on Mn depleted thylakoids isolated from spinach leaves. After various exposures to photoinhibitory light, the chlorophyll-protein complexes of both photosystems I and II were separated by sucrose gradient centrifugation and analysed by Western blotting, using a set of polyclonals raised against various apoproteins of the photosynthetic apparatus. A series of events occurring during donor side photoinhibition are described for photosystem II, including: (a) lowering of the oligomerization state of the photosystem II core; (b) cleavage of 32-kD protein D1 at specific sites; (c) dissociation of chlorophyll-protein CP43 from the photosystem II core; and (d) migration of damaged photosystem II components from the grana to the stroma lamellae. A tentative scheme for the succession of these events is illustrated. Some effects of photoinhibition on photosystem I are also reported involving dissociation of antenna chlorophyll-proteins LHCI from the photosystem I reaction center.

Apoproteins↗

PubMed1980

Structural changes of human epidermal alpha-keratin in disorders of keratinization.

The chemistry and structure of the epidermal alpha-keratin extracted from the skin of patients with a variety of disorders of keratinization have been investigated using biochemical, biophysical, and electron microscopic techniques developed for the characterization of normal mammalian epidermal keratin. Generally, the alpha-keratin polypeptides of the diseased epidermis differed from those of uninvolved epidermis or of normal volunteers in having varying numbers of polypeptide components of lower molecular weights, numerous free amino acids, higher contents of alpha-helix, and only limited facility for polymerization in vitro into native-type epidermal keratin filaments. As the alpha-helix-enriched fragments, which represent up to two-thirds of the polypeptide chains, isolated after limited tryptic digestion of the keratin filaments of normal, uninvolved, and involved epidermis, were physicochemically identical, it seems that the end-terminal non-alpha-helical regions of the polypeptides of diseased epidermis are abnormal. These differences may be a result of degradation or of altered protein synthesis.

Amino Acid Sequence↗

PubMed1978

Structural changes in the T4 gene 32 protein induced by DNA polynucleotides.

Alterations in the structure of the DNA-binding protein specified by gene 32 of bacteriophage T4 have been detected using partial trypsin digestion as a conformational probe. Limited tryptic hydrolysis of the gene 32 protein removes a fragment ("B" region), of 21 amino acids from the NH2 terminus and a 6,200-dalton fragment ("A" region) from the COOH terminus. Poly(dT), poly(dC), and single-stranded DNA increase the rate of tryptic hydrolysis of the "A" region but decrease the rate of tryptic hydrolysis of the "B" region. Oligonucleotides, which are too short to permit cooperative binding of the gene 32 protein, do not alter the rate of tryptic hydrolysis of either the "A" or "B" regions. A model which accounts for these findings requires that the "B" region be involved in gene 32 protein:gene 32 protein interactions when the gene 32 protein: DNA complex is formed. As a consequence of the gene 32 protein:DNA interaction, the "A" region should be able to participate more effectively in vivo and in vitro with other proteins involved in T4 DNA metabolism.

Amino Acid Sequence↗