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PubMed1995

Structural changes in base-paired region 28 in 16 S rRNA close to the decoding region of the 30 S ribosomal subunit are correlated to changes in tRNA binding.

Escherichia coli 30 S ribosomal subunits undergo a reversible change under low monovalent or divalent cation concentration and become inactive in tRNA binding and 50 S subunit association. In the inactive form, 16 S rRNA base-pairs (921-922).(1395-1396) and (923-925).(1391-1393), which are part of region 28, are unstable and an alternate arrangement, (921-923).(1532-1534), is detected by psoralen photochemical crosslinking. Site-directed mutagenesis has been used to investigate whether changes in base-paired region 28 or the alternate secondary structure is responsible for the inactivity of the subunit. 30 S subunits with the substitution C1533A or with deletion of nucleotides 1534 to 1542 can still be inactivated like the wild-type 30 S subunit. On the other hand, 30 S subunits that contain sequence changes in the 920 to 926 region show moderate to severe decreases in tRNA binding even under activating conditions. When 30 S subunits containing these mutations were subjected to chemical probing, they failed to show the normal hyper-reactivity of nucleotide G926 and, instead, reactivity was shifted to G925 or to G928, and G929. Two mutations in the 920 region result in structures in which A1394 is base-paired rather than being unpaired as normal; deletion but not substitution of A1394 resulted in loss of tRNA binding activity and depression of the reactivity of G926. Mutations were made to insert or delete a nucleotide at position 920. The deletion mutant but not the insertion mutant has decreased tRNA binding activity and also low reactivity of G926. We conclude that structural changes in region 28 account for the active/inactive difference in tRNA binding. Molecular models of region 28 were made using the program MC-SYM. Models that include a hydrogen bond interaction between A1394 and G1392 account for the G926 reactivity in the wild-type sequence and account for the effects of most of the mutations in changing the G926 reactivity.

Aldehydes↗
PubMed1994

Altered nucleus/cytoplasm relationship and degenerative structural changes in human dilated cardiomyopathy.

We investigated systematically the structure of the myocardium obtained from patients with dilated cardiomyopathy undergoing transplantation because of intractable heart failure. Hearts were explanted at the time of surgery from 12 patients (10 men and 2 women, aged 31-57 years, ejection fraction < 20%) and numerous samples were taken for light and electron microscopy. Biopsies from the left ventricle of 8 patients during operations for atrial septal defect served as control tissue. The most obvious qualitative findings were focal hypertrophy and atrophy of myocytes, enlargement and bizarre shape of nuclei, lack of contractile material and occurrence of numerous small mitochondria. On a quantitative level, the nuclear density was reduced (18%, p < 0.05) but the nuclear profile area was significantly increased (85%, p < 0.001). Thus the nucleus/cytoplasm relationship was altered. The volume density of the contractile filaments was decreased (25%, p < 0.001), but the mitochondrial volume density was unchanged. There was an increase in cell width (39%, p < 0.01) and of the connective tissue content (= fibrosis) (112%, p < 0.001). It is suggested that the nuclear abnormalities may be the primary event in the pathogenesis of dilated cardiomyopathy. These may then lead to a reduced transcriptional rate which most probably is the cause of the lack of myofilaments and other degenerative changes. The deterioration of the structural quality of the hypertrophied myocytes results finally in atrophy and fibrosis and may be the structural correlate of functional disturbances in dilated cardiomyopathy.

Adult↗
PubMed1996

Structural changes of beta-lactoglobulin B induced by urea. Evidence of residual structure.

Several spectroscopic methods have been used to study the structure of beta-lactoglobulin B at pH 2.1 in the presence of 8M urea. Fluorescence and polarization of fluorescence spectroscopy measurements indicate that the two tryptophanyl residues of the protein are exposed to the solvent in the denatured state. CD in the far-UV indicates that the amount of secondary structure in the denatured state is comparable to that found in the native state, whereas the CD spectrum in the near-UV shows that the tertiary structure is not completely disordered. The results of one-dimensional 1H NMR spectroscopy show that some local non-random structure is maintained in the denatured state, but most of the polypeptide chain has an extended non-globular conformation under the conditions of the present experiments. This conclusion is reinforced by the results of two-dimensional 1H NMR conducted on denatured samples of beta-lactoglobulin B. The study of states with intermediate levels of order will aid the understanding of how the native structure of beta-lactoglobulin B is organised during the refolding pathways.

Animals↗
PubMed1982

[Structural changes in the thymus in experimental tuberculosis].

Structural and functional alterations in the thymus in experimental tuberculosis are phasic in nature and involve 2 stages. In the early stage of tuberculous process, the morphofunctional status of cell elements of the blood-thymic barrier increases as vascular permeability and lymphocyte migration rise and the synthesis of epithelial cells of the medulla gets activated. During disseminated tuberculosis cell elements of the thymic parenchyma undergo destructive changes as a result of histohematic barrier impairment leading to disturbed homeostasis and organ alterations. Thymic macrophages develop from monocytes rather than from local cells.

Animals↗
PubMed2000

Structural changes and protein expression in the mastoid bone adjacent to cholesteatoma.

OBJECTIVE: Cholesteatoma of the mastoid and middle ear causes erosion of nearby bone. In this study we examined the mastoid bone adjacent to cholesteatoma and compared it with normal mastoid bone. In particular, noncollagenous proteins, which have a special structural and functional role in bone, were addressed. STUDY DESIGN: Nine mastoid specimens with cholesteatoma and four normal specimens obtained at surgery were examined. METHODS: Histological and immunohistochemical methods were employed to evaluate the nature of structure and noncollagenous protein content changes in the mastoid bone affected by cholesteatoma. RESULTS: The bone associated with cholesteatoma had structural changes as a noncontinuous periosteum, empty lacunae, irregular cement lines, and, specifically, the appearance of eosinophilic vesicles at the interface between the bone and cholesteatoma Immunohistochemistry demonstrated that noncollagenous proteins were apparently absent in the affected mastoid bone. Bone remote from the cholesteatoma seemed normal. CONCLUSIONS: These findings demonstrate for the first time the changes in the noncollagenous protein content in the mastoid bone affected directly by cholesteatoma These changes could be a result of a direct influence of cholesteatoma-derived products on the osteoblast.

Adolescent↗
PubMed2004

Secondary structure change of oligonucleotide induced by salts.

Formation of a unimolecular structure is essential for many biological processes such as transcription and translation, and the (deoxy)ribozyme activities. Since such nucleic acids consist of self-complementary sequence, they also have a potential to form a bimolecular structure as well. In this study, we designed 13 RNA and DNA sequences which can potentially form a hairpin loop structure by one strand and a duplex by two strands. On the basis of the UV melting and CD spectra measurements, we found that an RNA oligomer of rGCAAGCAAGCUUGC adopted different secondary structures depending on NaCl concentration, for example, a duplex at 1 M NaCl and a hairpin loop structure at 10 mM NaCl. On the other hand, the structure of DNA oligomer with the same sequence was unchanged. This observation indicates that the structural transition by the change of the NaCl concentration is not due to the nature of the sequence.

Buffers↗
PubMed1979

[Structural changes in spores under high temperature exposure].

The electron microscopy of ultrathin sections of B. cereus spores showed that no lysis and destructive changes occurred in the main structural components of the spores when heated to 99 degrees C (in distilled water). By the time 99% of the population were destroyed, the spores seemed to preserve the exosporium of the sporoderm, the cortex and the sporoblast intact. Even autoclaving at 120 degrees C for 15 min brought about no visible changes in the ultrastructure of the spores, though it killed the whole spore population.

Bacillus cereus↗
PubMed1991

[The aging of the heart: weight and structural changes in the left ventricle with age].

Structural alterations of the cardiovascular system with aging are difficult to differentiate from superimposed pathologic processes. To determine whether aging "per se" affects the dimension of the heart, the weight of the heart, and the left ventricle and their rations to body weight, left ventricle wall thickness, the number of myocyte nuclei in the ventricle and the myocyte cell volume per nucleus were measured in 67 autopsies of subjects, 45 males and 22 females, who died from causes independent of cardiovascular diseases, from 17 to 90 years old. With aging, total heart weight increased slightly, while left ventricular and interventricular septum weights after dissection of the subepicardial fat decreased significantly (r = 0.44; p less than 0.001). Although left ventricular wall thickness remained constant with time, left ventricular weight to body weight ratio decreased progressively. At the structural level the number of myocyte nuclei within the left ventricle decreased (r = 0.45; p less than 0.001), whereas myocyte cell volume per nucleus increased (r = 0.30; p greater than 0.05) with age. Thus, the aging process of the heart is associated with a reduction in volume of the myocardial mass resulting from myocyte cell loss and reactive hypertrophy of the spared myocytes.

Adolescent↗
PubMed1988

Structural changes in nuclear chromatin in rat pituitary after chronic stress of low intensity.

Acute, intense sources of "psychogenic" stress clearly modify the structure and function of the hypophysis, and there are concomitant changes in many peripheral physiological systems. Less dramatic sources of stress yield more equivocal results. An experiment is reported in which nuclear morphology of adenohypophyseal cells from 49 male rats exposed to a chronic, low-intensity stressor was examined both by conventional histological and computer-assisted-image-processing methods. The hypothesis tested was that an unequivocal pattern of morphological changes in the nucleus and nuclear chromatin would be revealed by image processing. Rats were killed after living for a year in a relatively low-stress environment, "crowded" in groups of five animals per cage. The control condition was a minimal stress environment of two rats per cage. Results suggested few signs of pathology from peripheral measures of hypophyseal activity, and direct light microscopic examination of the gland revealed no differences between the two groups. Analysis of computer-enhanced images of the pars distalis nuclei from the adenohypophysis, on the other hand, generated findings that were statistically and biologically significant. Nuclear size increased in the stress condition, the number of chromatin and area occupied by the particles increased, and the position of chromatin shifted toward the periphery of the nucleus. Perhaps more important, optical density analysis indicated that chromatin was less tightly packed in the experimental animals. Implications are that chronic, low-intensity stress modulates nuclear structural changes from a dormant to an active state that portend changes in the peripheral systems influenced by the hypophysis.

Adrenal Glands↗
PubMed1985

Structural changes of hair after incorporation of the proline analogue L-azetidine-2-carboxylic acid. A model of hair disease by alteration of primary structure.

In order to correlate biochemical changes of the hair with physical properties we present a model for the examination techniques. L-azetidine was incorporated into the hair keratin complex and the resulting mechanoelastic properties were determined using the ultramicrohardness testing system on scanning electron microscopy. Structure was investigated by X-ray diffraction and incorporation of L-azetidine was detected by thin-layer chromatography. This system could possibly be introduced for examination of hair changes in humans. 8 white mice, 3 weeks of age, were given L-azetidine-2-carboxylic acid in water (0.1 g/100 ml) as only source of fluid over a period of 5 weeks. They had free access to dry mouse cake only. 8 animals of the same strain, who had free access to tap water and mouse cake and were kept under the same conditions, served as controls. After 5 weeks, the animals were sacrificed and hair was obtained for analyses. 2 dimensional thin-layer chromatography of hair hydrolyzed with 6N HCl at 105 degrees C for 12 hours revealed 2 additional spots in the chromatographic pattern in the experimental animals in comparison with the control group. 1 of the spots was identified as L-azetidine-2-carboxylic acid, while the second spot was possibly a degradation product of L-azetidine on acid hydrolysis at a high temperature. Hair of the animals was put into Mark capillaries and subjected to X-ray diffraction, which showed a markedly disordered orientation of keratin. Impression studies using scanning electron microscopy revealed a remarkably reduced elasticity of hair with incorporated L-azetidine. These findings may be explained on the basis of qualitative or quantitative changes in the helical structure of the keratin complex of hair, which is responsible for the elastic properties, whereas the globular matrix is responsible for the firmness of the hair.

Animals↗
PubMed1979

Gross structural changes in isolated liver cell plasma membranes upon binding of insulin.

The addition of 10(-9) M insulin to a suspension of rat liver plasma membranes increases the overall lipid microviscosity, eta, by about 10--20%. The effect is confined to physiological concentrations of the hormone and is highly specific. The specificity was demonstrated in experiments where insulin analogues were added to liver plasma membranes and where insulin was added to human erythrocyte membranes. In both of these experiments practically no change in eta was detected. Upon in vitro enrichment of the membrane cholesterol, eta exceeded the level mediated by insulin binding, and the addition of 10(-9) M insulin to the cholesterol-enriched membranes did not further increase eta. Concomitant to the increase in eta upon insulin binding, the overall degree of exposure of the membrane protein, presumably to both sides of the membrane, is substantially increased. This effect is in line with the notion of vertical displacement of membrane proteins induced by changes in eta. The observed structural modulation can account for the effect of insulin on unrelated membrane responses, as well as for the negative cooperativity of insulin binding.

Animals↗
PubMed2004

Structural change of the heme pocket due to disulfide bridge formation is significantly larger for neuroglobin than for cytoglobin.

Human neuroglobin (hNgb) and human cytoglobin (hCygb), two recently discovered members of the vertebrate globin family, are known to be able to form an intramolecular disulfide bridge. Using electron paramagnetic resonance (EPR), we show that formation of a disulfide bridge in ferric hNgb causes a considerable change in the heme pocket structure, whereas this is not so clear for ferric hCygb. The structural results can be related nicely to earlier histidine and dioxygen affinity studies of the ferrous proteins.

Cytoglobin↗
PubMed1980

Lack of gross protein structure changes in the working cycle of (Na+, K+)-dependent adenosinetriphosphatase. Evidence from infrared and intrinsic fluorescence spectroscopy data.

Infrared and tryptophan fluorescence spectra of practically all sufficiently stable functional complexes of a highly purified preparation of membrane-bound (Na+, K+)-dependent ATPase have been measured. The formation of any functional complex was not accompanied by any considerable change of either shape or position of the tryptophan fluorescence spectrum. Only in the presence of adenine nucleotides was there a small decrease of fluorescence intensity (by 5-8%), which apparently results from a change of the sample light scattering. Analysis of the results obtained leads to the conclusion that the environment of no more than one or a few tryptophan residues may differ in all the (Na+, K+)-ATPase complexes studies. A comparison of infrared protein spectra in the region of amide I band showed that at any wavenumber the differences between them did not exceed 3% of the maximum absorption. This means that no more than 3% of protein peptide groups can change their conformation upon transition between the enzyme functional states. These results, obtained by two independent techniques, allow us to conclude that even if changes of the internal protein structure occur during the working cycle of this transport system, if they have an extremely local character.

Adrenal Medulla↗
PubMed1994

Radiological and histological analysis of the structural changes in the rat parotid gland following release of Stensen's duct obstruction.

Sialography is the preferred method for diagnosis and treatment planning in obstructive sialadenitis. Although many experimental studies have reported changes following duct obstruction, those following release of obstruction have not been examined. The present study was undertaken to clarify: (1) the relationship between sialographic and histological changes; (2) the effects of duration and pressure of obstruction on gland recovery; (3) the possibility of establishing those sialographic features which indicate the prognosis for gland recovery. Stensen's ducts of rat parotid glands were obstructed for two different periods and at three different pressures in order to induce varying degrees of degenerative changes in the gland. The structural alterations resulting from release of obstruction were investigated by means of qualitative and quantitative microsialography and histology. Gland structure was assessed visually from the latter and classified into six groups: normal, recovery, and slight, moderate and severe degeneration and fibrous. Microsialograms were evaluated based on these groups. Qualitatively, microsialograms of the operated glands had a stricture in the obstructed region and dilation of the major ducts. Histological differences between recovery and degeneration glands were reflected in the morphology of peripheral ducts. The former showed a branch-like morphology similar to that of the normal group, and the latter contained small granule-like structures. Quantitatively, dilation of major ducts in the recovery group decreased compared with the other operated groups. There were no distinct sialographic features in the degeneration and fibrous groups which correlated with the degree of degeneration observed histologically. Duration and pressure of obstruction were highly predictive for prognosis for recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[Structural changes in human dentin with the use of modern filling materials].

Changes in human dentin surface structure, effected by potassium oxalate, potassium nitrate, calcium hydroxide, were studied by scanning electron microscopy. Crystal layers of different structures with complete or partial occlusion of the dentin tubes were detected. Complete occlusion was achieved only if potassium oxalate was used.

Calcium Hydroxide↗
PubMed2002

Does fusion of domains from unrelated proteins affect their folding pathways and the structural changes involved in their function? A case study with the diphtheria toxin T domain.

We investigated whether the structural and functional behaviors of two unrelated protein domains were modified when fused. The IgG-binding protein ZZ derived from staphylococcal protein A was fused to the N- and/or C-terminus of the diphtheria toxin transmembrane domain (T). T undergoes a conformational change from a soluble native state at neutral pH to a molten globule-like state at acidic pH, leading to its interaction with membranes. We found that this molten globule state was not connected to the GdnHCl-induced unfolding pathway of T. The pH-induced transition of T, and also the unfolding of T and ZZ at neutral and acidic pH, were unchanged whether the domains were isolated or fused. The position of ZZ, however, influenced the solubility of T near its pK(i). SPR measurements revealed that T has a high affinity for membranes, isolated or within the fusion proteins (K(D)< 10(-11) M). This work shows that in the case of T and ZZ, the fusion of protein domains with different stabilities does not alter the structural changes involved in folding and function. This supports the use of T as a soluble membrane anchor.

Circular Dichroism↗