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PubMed2002

An NMR study of O-glycosylation induced structural changes in the alpha-helix of calcitonin.

We previously reported that two out of seven artificially O-glycosylated calcitonin derivatives had an altered peptide backbone conformation as indicated by decreased helical contents, determined by CD measurement. In the present study, two of those derivatives, in which a GalNAc residue is attached to Thr6 or Thr21 of calcitonin, were analyzed by NMR in order to determine the structural changes induced by the O-glycosylation in more detail. Deviations in the chemical shifts suggest that the structural change is not global but only a local one and is located in the vicinity of each O-glycosylation site. The intensities of the NOE cross peaks, an indicator of alpha-helical structure, also were decreased around the O-glycosylation site. The hydrogen/deuterium exchange rates of the main chain amide protons increased at the N- or C-terminal portion of the alpha-helix corresponding to the respective O-glycosylation site and explains the results of the CD experiments. The inter-residual NOE cross peaks between the carbohydrate and the peptide portions, other than the O-glycosylated amino acid residue, showed that local structural contacts extended three or two residue distance for Thr6- or Thr21-glycosylated derivative, respectively. Thus, we conclude that the O-glycosylation induced a change in the local structure and that this structural perturbation modulated the original alpha-helical structure of calcitonin, resulting in the apparent decrease in the helical content deduced from CD spectra.

Amino Acid Sequence↗
PubMed1986

The kinetic and structural changes of the mitochondrial F1-ATPase with temperature.

Mitochondrial F1-ATPase shows a break in the Arrhenius plot with an increase of the activation energy below 17 degrees C, this may imply that the F1-ATPase undergoes a conformational change at this temperature. Further, a structural change of the F1-ATPase is indicated by analysis of the intrinsic fluorescence at 307 nm between 33 and 11 degrees C and also by evaluation of the circular dichroism spectra of the enzyme at temperatures below and above the temperature corresponding to the discontinuity of the Arrhenius plot. It is therefore suggested that F1-ATPase exists in two temperature dependent conformational states to which different catalytic properties may be assigned.

Adenosine Triphosphate↗
PubMed1980

Structural changes induced by tetracycline in secretory ameloblasts in young rats.

The effects of tetracycline hydrochloride (TC) on secretory ameloblasts in mandibular incisors and first molars in young rats were investigated. The pathogenesis of the TC-induced changes was examined in light and electron microscopes 6, 12, 24 and 96 h after a single intraperitoneal injection of a high dose of TC (200 mg TC/kg body wt.) into 4-d-old animals. Secretory ameloblasts from non-injected animals served as controls. Cellular changes were observed in all teeth 6 h after injection. The changes increased with the postinjection period and after 96 h they were so severe that they were considered irreversible. The incipient changes of the ameloblasts comprised altered structure and location of the mitochondria, succeeded by dilated cisternae of endoplasmic reticulum arranged in short curled formations. Later on, distorted Golgi complexes were observed. Secretory granules appeared in various numbers in the Golgi zone and in the Tomes' processes. In severely affected ameloblasts the cell nuclei showed an increased content of chromatin. Autophagic vacuoles and extracellular membrane bound fragments with cellular remnants were frequent, indicating death of some of the ameloblasts. Areas of stippled secretory material were observed along the formative enamel front and in extracellular spaces between the ameloblasts. In the 96-h group calcified bodies with a varying content of crystals were scattered between the cells. Incisors and the molars displayed similar patterns of structural changes of the secretory ameloblasts; however, the changes developed earlier and became more severe in the molars.

Ameloblasts↗
PubMed1971

Structural changes in Clostridium botulinum type E after treatment with boticin S5 1 .

Treatment with boticin S5(1), a bacteriocin produced by a nontoxigenic organism closely related to Clostridium botulinum type E, caused extensive changes in the structure of a sensitive C. botulinum type E strain. Nucleoid deoxyribonucleic acid, normally seen as fine filaments scattered throughout the cell, was aggregated into dense deoxyribonucleic acid masses. Mesosomes appeared to undergo structural rearrangement from lamellar to vesicular configuration. Eventual dissolution of cell contents left bacterial ghosts composed of seemingly intact cell walls with remnants of the cytoplasmic membrane and internal structures. The morphological changes observed in boticin-treated strain 070 cells were very similar to those produced by a bacteriocin-like substance from phage type 71 Staphylococcus aureus on sensitive beta-hemolytic streptococci. A similarity in the mode of action of the two bactericidal agents is suggested.

Bacteriocins↗
PubMed1985

[Various patterns in structural changes in the cortex and subcortical structures of the human brain during the aging process].

The authors examined the structural organization of cortical and subcortical formations (fields 4, 6, 8, 44, 47, 39, the head of the caudate nucleus and thalamic nuclei) of the right and left hemispheres of the brain of 6 mentally normal subjects aged 30 to 90 years. In sections 20 millimicron thick and stained by Nissl's method the authors measured the density of neurons in subcortical nuclei, in layers III and V of the cortical fields, as well as the number of neurons containing lipofuscin. The identified characteristics indicate heterochronicity of the process of ageing in different portions of the brain: motor and, particularly, cortical structures are involved in this process earlier and more intensively than others.

Adult↗
PubMed1997

Desensitization of the nicotinic acetylcholine receptor mainly involves a structural change in solvent-accessible regions of the polypeptide backbone.

The difference between infrared spectra of the nicotinic acetylcholine receptor (nAChR) recorded using the attenuated total reflectance technique in the presence and absence of carbamylcholine exhibits a complex pattern of positive and negative bands that provides a spectral map of the structural changes that occur in the nAChR upon agonist binding and subsequent desensitization. Two relatively intense bands are observed in the amide I region of the difference spectra recorded in 1H2O buffer near 1655 cm(-1) and 1620 cm(-1) that were previously interpreted in terms of either a net conversion of beta-sheet to alpha-helix or a reorientation of transmembrane alpha-helix accompanied by a change in structure of beta-sheet and/or turn [Baenziger, J. E., Miller, K. W., & Rothschild, K. J. (1993) Biochemistry 32, 5448-5454]. However, difference spectra recorded in 2H2O buffer reveal that these and other difference bands in the amide I region undergo downshifts in frequency upon peptide 1H/2H exchange that are much larger than the downshifts in frequency that are typically observed for the amide I vibrations of either alpha-helix or beta-sheet. Difference spectra recorded in 2H2O buffer within either minutes or hours of prior exposure of the nAChR to 2H2O exhibit the same amide I difference band shifts that are observed in difference spectra recorded after 3 days prior exposure of the nAChR to 2H2O. Most of the peptides that are involved in both ligand binding and the resting to desensitized conformational change and that give rise to bands in the difference spectra therefore exchange their hydrogens for deuterium on the seconds to minutes time scale. The frequencies of the difference bands, the magnitudes of the difference band shifts upon peptide 1H/2H exchange, and the rapidity of the hydrogen deuterium exchange kinetics of those structures that give rise to amide I bands in the difference spectra all suggest that the formation of a channel-inactive desensitized state results predominantly from a conformational change in solvent-accessible extramembranous regions of the polypeptide backbone as opposed to a large structural perturbation near the ion channel gate. A conformational change in the agonist binding site may be primarily responsible for channel inactivation upon desensitization.

Carbachol↗
PubMed1999

Structural changes of dental enamel in both dentitions of cleft lip and palate patients.

The aim of this study was to register the incidence, the location and the character of structural changes in dental morphology in cleft lip and palate patients and to examine the connection between defects of dental enamel and the development of clefts. Twenty-two children and adolescents from a cross-section study carried out in 1987/89 with cleft lip and palate patients could be covered in a second study (longitudinal study). The frequency, the extent and the location of changes of dental hard tissues in both dentitions were assessed in the form of a static and a dynamic examination. Dental enamel anomalies were found in all patients, with opacities of cleft-adjacent incisors being the dominating form of classified defects in both dentitions. In 20 of the 22 examined patients, dental enamel dysplasia was found both in the primary and in the secondary dentition. The intraindividual comparison of the maxillary teeth in both dentitions showed that 19 patients had at least 1 permanent tooth retaining the structural changes in the dental enamel. The location of the defect and the fact that both dentitions were involved reflect the moment of effectiveness of pathogenetic stimuli. Consequently this can be interpreted as the outcome of corresponding pathomechanisms both for disorders of the dental structure and for the development of the primary palate.

Adolescent↗
PubMed1989

[Physiopathology of arterial hypertension. Significance of the renin-angiotensin-aldosterone system and structural changes].

It is presented a review of some recent aspects of the hypertension's physiopathology, namely those related with the renin-angiotensin-aldosterone system and with the cardiovascular structural changes. The large action range of the angiotensin is pointed out, in particular those actions related with the heart's and vessel's adaptation to a chronic load of pressure. In the end, the author stresses some recent references about the genetic's role on the pathogenesis of the structural changes.

Angiotensin II↗
PubMed1997

NMR studies of Ca2+ binding to the regulatory domains of cardiac and E41A skeletal muscle troponin C reveal the importance of site I to energetics of the induced structural changes.

Ca2+ binding to the N-domain of skeletal muscle troponin C (sNTnC) induces an "opening" of the structure [Gagné, S. M., et al. (1995) Nat. Struct. Biol. 2, 784-789], which is typical of Ca2+-regulatory proteins. However, the recent structures of the E41A mutant of skeletal troponin C (E41A sNTnC) [Gagné, S. M., et al. (1997) Biochemistry 36, 4386-4392] and of cardiac muscle troponin C (cNTnC) [Sia, S. K., et al. (1997) J. Biol. Chem. 272, 18216-18221] reveal that both of these proteins remain essentially in the "closed" conformation in their Ca2+-saturated states. Both of these proteins are modified in Ca2+-binding site I, albeit differently, suggesting a critical role for this region in the coupling of Ca2+ binding to the induced structural change. To understand the mechanism and the energetics involved in the Ca2+-induced structural transition, Ca2+ binding to E41A sNTnC and to cNTnC have been investigated by using one-dimensional 1H and two-dimensional {1H,15N}-HSQC NMR spectroscopy. Monitoring the chemical shift changes during Ca2+ titration of E41A sNTnC permits us to assign the order of stepwise binding as site II followed by site I and reveals that the mutation reduced the Ca2+ binding affinity of the site I by approximately 100-fold [from KD2 = 16 microM [sNTnC; Li, M. X., et al. (1995) Biochemistry 34, 8330-8340] to 1.3 mM (E41A sNTnC)] and of the site II by approximately 10-fold [from KD1 = 1.7 microM (sNTnC) to 15 microM (E41A sNTnC)]. Ca2+ titration of cNTnC confirms that cNTnC binds only one Ca2+ with a determined dissociation constant KD of 2.6 microM. The Ca2+-induced chemical shift changes occur over the entire sequence in cNTnC, suggesting that the defunct site I is perturbed when site II binds Ca2+. These measurements allow us to dissect the mechanism and energetics of the Ca2+-induced structural changes.

Animals↗
PubMed1997

Long-term inhibition of the renin-angiotensin system in genetic hypertension: analysis of the impact on blood pressure and cardiovascular structural changes.

OBJECTIVE: To compare, using data from published studies, the efficacy of chronic inhibition of the renin-angiotensin system in inducing persistent downregulation of hemodynamic and cardiovascular structural changes in an adult rat with established genetic hypertension with the widely accepted known downregulation in young genetically hypertensive rats. STUDY SELECTION: We report on 36 studies that satisfied our inclusion criteria (angiotensin converting enzyme inhibitor or angiotensin II receptor antagonist treatment that lowered arterial pressure levels for at least 3 weeks). Of the 24 studies concerning developing hypertensive rats, a significant number (n = 17) also examined the persistence of any hemodynamic or cardiovascular effects after withdrawal of treatment. Conversely, of 15 studies using adult rats only seven and three reported on post-treatment hemodynamic and cardiovascular structural indices respectively. RESULTS: During treatment the hemodynamic and cardiovascular structural changes produced were qualitatively and quantitatively similar in the young and adult treated rats. Critical assessment of the persistence of these effects after withdrawal of treatment again found qualitatively similar responses. However, the strength of this finding is limited by the paucity of studies concerning adult rats in which equivalent treatment durations and equipressor doses of treatments were compared between these two age groups. CONCLUSIONS: Blockade of the renin-angiotensin system appears to have an efficacy in reversing established hypertension and hypertrophy similar to that with which it prevents the development of hypertension and hypertrophy. This partial 'cure' of hypertension after withdrawal of treatment is clearly evident when treatment is initiated during the development of hypertension and appears to be similar even when treatment is initiated in established hypertension.

Angiotensin Receptor Antagonists↗
PubMed1990

Regulation and quaternary structural changes in rabbit muscle phosphofructokinase.

Subunit assembly plays a significant role in the regulation of rabbit muscle phosphofructokinase (PFK), although conformational changes and post-translational modifications have also been implicated to regulate the enzyme activity. In the absence of high-resolution structural information, the three-dimensional arrangements of subunits in the rabbit muscle PFK in its active and inactive states are not known. Hence, a systematic study is initiated, and phosphorylation of PFK subunit is employed as a probe for the structure-function correlation of the enzyme. The self-association of the phosphorylated and dephosphorylated PFK was monitored by sedimentation velocity at pH 7.0 and 23 degrees C. Results show that both the phosphorylated and dephosphorylated forms of PFK exhibit the same mechanism of assembly. The secondary structures of both forms of PFK were monitored by circular dichroism (CD) as a function of protein concentration ranging from 20 to 2000 micrograms/ml. Results show that there is no detectable difference in the structure under all experimental conditions. The accessibility of tryptophan to solvent was monitored by fluorescence quenching within the same range of protein concentration. Results show that the fluorophores are more accessible to the quencher at higher protein concentrations. Hence, post-translational modification and subunit association do not induce significant structural change in PFK subunit, although the accessibility of tryptophan residues is altered with oligomer formation. Furthermore, sedimentation and CD studies show that the activation of PFK by substrate includes no detectable modification in secondary/tertiary structure but a quaternary structural change, and the local environments of some, if not all, of the tryptophan residues are less accessible to solvent. Hence, the change in sedimentation behavior between the active and inactive tetrameric PFK is due to a rearrangement of subunit-subunit interactions. In order to correlate the physical properties of PFK to the regulatory behavior of enzyme activity, the steady-state kinetics were investigated under the same experimental conditions. In conditions where enhancement of self-association is observed, the kinetic behavior reflects activation of the enzyme. Hence, this correlation between subunit assembly and the regulation of enzyme activity in PFK must reflect an intrinsic property of the muscle enzyme.

Animals↗
PubMed2000

Structural changes of the substantia nigra in Parkinson's disease as revealed by MR imaging.

BACKGROUND AND PURPOSE: The possibility of using MR imaging as a sensitive marker of the structural changes in Parkinson's disease has been a long-sought goal. We describe a new method for imaging and quantifying the morphologic changes of the substantia nigra in Parkinson's disease and compare radiologic findings with clinical evaluation. METHODS: Using a combination of two MR imaging inversion-recovery pulse sequences, the substantia nigra was imaged in six patients with Parkinson's disease and six age-related control participants. A radiologic index was defined and used to quantify the signal changes that were observed in the patients. The radiologic index was compared with clinical scores obtained from the Unified Parkinson's Disease Rating Scale. RESULTS: The images showed loss of signal in a lateral-to-medial gradient in cases of Parkinson's disease, corresponding to the known neuropathologic pattern of degeneration. The radiologic index was highly correlated with the Unified Parkinson's Disease Rating Scale score, and there was no overlap in radiologic indices between the patient and the control groups (P < .00005). CONCLUSION: This study suggests that MR imaging is sensitive to structural changes in even the earliest cases of Parkinson's disease, thereby indicating the potential for detecting presymptomatic disease. Furthermore, a radiologic measure has been defined that correlates with the conventional clinical measure of disease severity. Therefore, MR imaging could prove to be a sensitive biological marker for objective staging of the disease.

Adult↗
PubMed2000

Secondary and tertiary structure changes of reconstituted LmrA induced by nucleotide binding or hydrolysis. A fourier transform attenuated total reflection infrared spectroscopy and tryptophan fluorescence quenching analysis.

LmrA, a membrane protein of Lactococcus lactis, extrudes amphiphilic compounds from the inner leaflet of the cytoplasmic membrane, using energy derived from ATP hydrolysis. A combination of total reflection Fourier transform infrared spectroscopy, (2)H/H exchange, and fluorescence quenching experiments was used to investigate the effect of nucleotide binding and/or hydrolysis on the structure of LmrA reconstituted into proteoliposomes. These measurements allowed us to describe secondary structure changes of LmrA during the catalytic cycle. The structure of LmrA is enriched in beta-sheet after ATP binding, and the protein recovers its initial secondary structure after ATP hydrolysis, when P(i) has been released. (2)H/H exchange and fluorescence quenching studies indicate that the protein undergoes two distinct tertiary structure changes during the hydrolysis process. Indeed, the protein alone is poorly accessible to the aqueous medium but adopts a more accessible conformation when ATP hydrolysis takes place. After ATP hydrolysis, but when P(i) is still associated with the protein, the accessibility is intermediate between these two states.

ATP-Binding Cassette Transporters↗
PubMed1986

Financing reform and structural change in the health services industry.

This paper reviews the major trends in financing reform, emphasizing their impact on those characteristics of the market for health services that economists have viewed as monopolistic, and discusses the implications of structural change for the allied health professions. Hopefully, by understanding the fundamental forces of change and responding to uncertainty with flexibility and imagination, the allied health professions can capitalize on the opportunities afforded by structural change. Overall, these trends should result in the long-term outlook for use of allied health services to increase at an average annual rate of 9% to 10%. Allied health professionals may also witness an increase in independent practice opportunities. Finally, redistribution of jobs will likely occur in favor of outpatient facilities, home health agencies, and nontraditional settings. This in turn will have an impact on allied health education, which will need to adapt to these types of reforms.

Allied Health Personnel↗
PubMedDate not supplied

Potent V2 vasopressin antagonists with structural changes at their C-terminals.

A variety of structural changes were made in the C-terminals of four potent antidiuretic (V2) antagonists. The parent analogs were all derivatives of [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid)]arginine-vasopressin, d(CH2)5AVP, namely d(CH2)5[D-Phe2,Ile4]AVP, d(CH2)5[D-Ile2,Ile4]AVP, d(CH2)5[D-Tyr(Et)2, Val4]AVP and d(CH2)5[D-Tyr(Et)2,Ile4]AVP. A number of amino acid amides were substituted for the C-terminal 9-glycinamide without reducing their V2-antagonistic potencies in rats. Many non-amino acid structures were also tolerated at the C-terminals of these antagonists and this end of these peptides can be prolonged without interfering with antagonistic potencies. Such altered V2-antagonists may be useful for the development of radioactive ligands, affinity labels and in affinity columns for studies on antidiuretic receptors. These C-terminal modifications also provide useful information for the further development of potent and specific V2-antagonists which can be valuable pharmacological tools and also promise to become useful clinically for the treatment of excessive water retention.

Animals↗
PubMed2002

Specific damage induced by X-ray radiation and structural changes in the primary photoreaction of bacteriorhodopsin.

Bacteriorhodopsin, the sole membrane protein of the purple membrane of Halobacterium salinarum, functions as a light-driven proton pump. A 3-D crystal of bacteriorhodopsin, which was prepared by the membrane fusion method, was used to investigate structural changes in the primary photoreaction. It was observed that when a frozen crystal was exposed to a low flux of X-ray radiation (5 x 10(14)photons mm(-2)), nearly half of the protein was converted into an orange species, exhibiting absorption peaks at 450 nm, 478 nm and 510 nm. The remainder retained the normal photochemical activity until Asp85 in the active site was decarboxlyated by a higher flux of X-ray radiation (10(16)photons mm(-2)). The procedure of diffraction measurement was improved so as to minimize the effects of the radiation damage and determine the true structural change associated with the primary photoreaction. Our structural model of the K intermediate indicates that the Schiff base linkage and the adjacent bonds in the polyene chain of retinal are largely twisted so that the Schiff base nitrogen atom still interacts with a water molecule located near Asp85. With respect to the other part of the protein, no appreciable displacement is induced in the primary photoreaction.

Bacteriorhodopsins↗
PubMedDate not supplied

[Structural changes in Candida lipolytica cells during citric acid biosynthesis].

The techniques of light and electron microscopy were used to study structural changes in Candida lipolytica cells related to limitation of their growth and a nitrogen source in medium with glucose and hexadecane and transition of the culture to the production of citric acids. Changes in the content of protein in the cell and in the activities of enzymes of the citrate and glyoxylate cycles located in mitochondria and peroxysomes of the yeast were investigated at the same time. The results characterizing cytological changes in the cell of C. lipolytica in the conditions of citric acid biosynthesis fit in well with the data on protein content and enzyme activities in the cells obtained by biochemical analysis. The transition of the yeast cells to the overproduction of citric acids has been shown to be related to profound rearrangements of the cell: the inhibition of protein synthesis; changes in the structure of the cytoplasm; the appearance of vacuoles of an irregular shape, often in contact with the mitochondria; changes in the mitochondrial and peroxysomal apparatus; the accumulation of lipids. It has been demonstrated once again that the peroxysomal apparatus of the yeast cell has a relationship with the metabolism of n-alkanes.

Candida↗