SEARCH · PubMed Health

Results for “Structural changes”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,243 records · Page 69Linked to original sources

PubMed2002

Intramolecular proton transfers and structural changes during the photocycle of the LOV2 domain of phototropin 1.

The phototropins are a family of membrane-associated flavoproteins that function as the primary blue light receptors regulating phototropism, chloroplast movements, stomatal opening, and leaf expansion in plants. Phot1, a member of this family, contains two FMN-binding domains, LOV1 and LOV2, within the N-terminal region and a C-terminal serine-threonine protein kinase domain. Light irradiation of oat phot1 LOV2 produces a cysteinyl adduct (Cys-39) at the flavin C(4a) position, which decays thermally back to the dark state. We measured pH and isotope effects on the photocycle. Between pH 3.7 and 9.5, adduct formation showed minimal pH dependence, and adduct decay showed only slight pH dependence, indicating that the pK values of mechanistically relevant groups are outside this range. LOV2 showed a nearly 5-fold slowing of adduct formation in D(2)O relative to H(2)O, indicating that the rate-limiting step involves proton transfer(s). Light-induced changes in the far UV CD spectrum of LOV2 revealed putative protein structural perturbations. The light minus dark CD difference spectrum resembles an inverted alpha-helix spectrum, suggesting that alpha-helicity is reversibly lost upon light irradiation. Decay kinetics for CD spectral changes in the far UV region occur at the same rate as those in the visible region, indicating synchronous relaxation of protein and chromophore structures.

Amino Acid Sequence↗

PubMed2006

Methanol-induced tertiary and secondary structure changes of granulocyte-colony stimulating factor.

We have studied methanol-induced conformational changes in rmethuG-CSF at pH 2.5 by means of circular dichroism (CD), fluorescence and infrared (IR) spectroscopy, and 8-anilino-1-naphthalene sulfonic acid (ANS) binding. Methanol has little effect on the secondary and tertiary structures of rmethuG-CSF when its concentration is in the range of 0 to 20% (v/v). At 30% (v/v) methanol, rmethuG-CSF has ANS binding ability. In the methanol concentration range of 30 to 70% (v/v) the amount of alpha-helix decreases a little, and the tertiary structure decreases significantly. At methanol concentrations above 70% (v/v), a transition to a more helical state occurs, while there is little change in the tertiary structure, and no ANS binding ability. Thermal denaturation studies involving CD have demonstrated that as the methanol concentration increases the melting temperature and the cooperativity of transition decrease, and the transition covers a much wider range of temperature. It seems that the decreased cooperativity means an increase in the concentration of partially folded intermediate states during the unfolding of rmethuG-CSF.

Anilino Naphthalenesulfonates↗

PubMed2000

[Structural changes in the cornea after LASIK-u during the early postoperative period].

PURPOSE: The study aimed to evaluate in vivo the corneal structure after refractive surgery and monitor morphologic and morphometric changes in the post-operative period. MATERIAL AND METHODS: The study included 35 eyes (25 patients) who underwent LASIK correction of myopia. The structure of the cornea was evaluated in vivo using a scanning slit confocal microscope. Each cornea was examined before, 2, 4 and 8 weeks after procedure. The keratocyte density was evaluated morphometrically in the anterior and posterior corneal stroma. RESULTS: Before surgery the keratocyte density in the anterior stroma ranged from 900 to 1200/mm2, while in the posterior stroma it ranged from 600 to 950/mm2. 8 weeks after LASIK the keratocyte density in anterior stroma ranged from 695 to 1048/mm2 and in posterior stroma from 565 to 935/mm2. CONCLUSIONS: After LASIK the keratocyte density decreases in anterior stroma while in posterior stoma it is constant.

Cell Count↗

PubMed2006

Changes in the level of poly(Phe) synthesis in Escherichia coli ribosomes containing mutants of L4 ribosomal protein from Thermus thermophilus can be explained by structural changes in the peptidyltransferase center: a molecular dynamics simulation analysis.

Data from polyphenylalanine [poly(Phe)] synthesis determination in the presence and in the absence of erythromycin have been used in conjunction with Molecular Dynamics Simulation analysis, in order to localize the functional sites affected by mutations of Thermus thermophilus ribosomal protein L4 incorporated in Escherichia coli ribosomes. We observed that alterations in ribosome capability to synthesize poly(Phe) in the absence of erythromycin were mainly correlated to shifts of A2062 and C2612 of 23S rRNA, while in the presence of erythromycin they were correlated to shifts of A2060 and U2584 of 23S rRNA. Our results suggest a means of understanding the role of the extended loop of L4 ribosomal protein in ribosomal peptidyltransferase center.

Amino Acid Sequence↗

PubMed2002

Structural change of ribosomes during apoptosis: degradation and externalization of ribosomal proteins in doxorubicin-treated Jurkat cells.

Changes in the amount and localization of human ribosomal proteins during apoptosis were determined. When total lysates of Jurkat cells undergoing apoptosis induced by doxorubicin were analyzed by Western blotting, degradation of three ribosomal proteins, S18, L5, and L14, was detected at 48 h after the induction of apoptosis. Decreases in the amounts of these three ribosomal proteins were also observed in ribosome-enriched fractions. These changes were partly abolished by the addition of the pan-caspase inhibitor z-VAD-fmk. Moreover, formation of the 80S ribosome complex appeared to be inhibited at 48 h after apoptosis induction. On the other hand, the rate of protein synthesis, assessed by measuring the incorporation of [35S]Met into bulk proteins, decreased as early as 12 h after the addition of doxorubicin. These results indicate that changes in the amount of ribosomal proteins and the overall structure of ribosomes in apoptosing cells occur after protein synthesis declines. Finally, analyses by flow cytometry, immunofluorescence, and Western blotting showed that six ribosomal proteins, S15, P0, L5, L6, L36a, and L41, were relocalized and expressed at the cell surface during apoptosis. The above results collectively indicate that ribosomes are structurally altered in apoptotic cells following inactivation of protein synthesis.

Antineoplastic Agents↗

PubMed1981

Structural changes of mitochondria in Chlamydomonas reinhardii after chloramphenicol treatment.

Ultrastructural and morphological alterations of mitochondria in the phytoflagellate Chlamydomonas reinhardii have been studied by use of serial sections after treatment with chloramphenicol. Remarkable volume changes could be observed as well as alterations in the internal fine structure of mitochondria. Under certain conditions, megamitochondria are formed with volumes exceeding 1 mum3. The changes, probably due to inhibition of mitochondrial protein synthesis, are described in some detail.

Cells, Cultured↗

PubMed1990

Time course of structural changes in regenerating electroreceptors of a weakly electric fish.

We examined the regenerating electroreceptors of the weakly electric fish Sternopygus by light and electron microscopy to search for possible structural correlates of known physiological changes that occur during regeneration (Zakon: J. Neurosci. 6(11):3297-3308, 1986) and to compare them with developing electroreceptors in larval fish (Vischer: Brain Behav. Evol. 33:223-236). Nine days after removal of a patch of cheek skin, new skin had filled the wound and undifferentiated precursor cell clusters were located in the epidermis just above the dermis. Nerve fibers were present near most, but not all, cell clusters. A few recognizable tuberous and ampullary precursor organs were seen at this time. Tuberous organs were composed of a group of large cells surrounded by smaller cells without a lumen and showed the beginning of a cellular plug. Ampullary organs appeared as a ball of cells with a small lumen opening into a nascent canal. Degenerating cells were found within organs, and sometimes entire organs degenerated. These were not innervated. By 2 weeks the large cells of the tuberous organ were developing into sensory cells, while the smaller cells were forming the capsule wall and the underlying basal cells. The characteristic tuberous organ canal filled with loosely packed epidermal cells was evident. The sensory cells of the ampullary organs were visible within the epithelial layer at the base of the lumen, and the large synaptic discs were beginning to form. The sensory cells and postsynaptic terminals contained numerous vesicles. The presynaptic vesicles, which appear in normal receptor cells, remained throughout regeneration and presumably underlie transmitter release. The postsynaptic vesicles appeared transiently in large numbers but declined to adult values by 4 weeks. We presume that these may serve a trophic role. By 3 weeks, organs generally appeared mature and began dividing into daughter organs. The formation of individual receptor organs during regeneration is similar to that observed in development. Receptor organs continued dividing until the appropriate number of organs per afferent was reached for the size of the fish. Although the organization of the receptors appeared generally normal, there were a few anomalies. Some afferents sent sprouts into the epidermis, and, as a result of such sprouting, some of these afferents innervated multiple organs over a greater distance than normal. This was first seen early in regeneration and persisted for as long as 5 months.(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗

PubMed2005

Phosphorylation and concomitant structural changes in human 2-Cys peroxiredoxin isotype I differentially regulate its peroxidase and molecular chaperone functions.

The H2O2-catabolizing peroxidase activity of human peroxiredoxin I (hPrxI) was previously shown to be regulated by phosphorylation of Thr90. Here, we show that hPrxI forms multiple oligomers with distinct secondary structures. HPrxI is a dual function protein, since it can behave either as a peroxidase or as a molecular chaperone. The effects of phosphorylation of hPrxI on its protein structure and dual functions were determined using site-directed mutagenesis, in which the phosphorylation site was substituted with aspartate to mimic the phosphorylated status of the protein (T90D-hPrxI). Phosphorylation of the protein induces significant changes in its protein structure from low molecular weight (MW) protein species to high MW protein complexes as well as its dual functions. In contrast to the wild type (WT)- and T90A-hPrxI, the T90D-hPrxI exhibited a markedly reduced peroxidase activity, but showed about sixfold higher chaperone activity than WT-hPrxI.

Amino Acid Substitution↗

PubMedDate not supplied

Structural changes in ocular trauma and the visual outcome.

This is the presentation of one year prospective study on the anatomical structural lesions in ocular traumas with their visual outcome among those cases admitted and treated at Nepal Eye Hospital, Kathmandu. The changing life style of the people and environmental changes around with the changing nature of the causative objects on eye injuries have been observed for causing more serious structural lesions or complications including loss of vision.

Adolescent↗

PubMed1984

An enzyme-probe method to detect structural changes in the myosin rod.

The temperature-dependence of local melting within the alpha-helical, coiled-coil structure of rabbit myosin rod has been investigated by following changes in the rate constants of proteolytic digestion. The kinetics of fragmentation of the rod by three different enzymes (alpha-chymotrypsin, trypsin and papain) over the temperature range 5 to 40 degrees C (pH 7, I = 0.5) has been monitored by electrophoresis of the digestion products on sodium dodecyl sulfate/polyacrylamide gels. All rate constants were corrected for the intrinsic temperature-dependence of the enzyme by comparison with model substrates. Results from the three enzyme-probes are similar in showing that local melting within the rod occurs in two distinct stages. At temperatures between 5 and 25 degrees C, melting is confined to a restricted segment of the rod structure near the light meromyosin/heavy meromyosin junction. At temperatures between 25 and 40 degrees C, a wider segment of the rod lysing between the junction and the short subfragment-2 segment (the hinge domain) appears to be melting, judging from the broad spectrum of cleavage sites observed in this region. Results are compared with those from other physicochemical methods that measure the hinging or opening of the coiled-coil structure of the rod.

Animals↗

PubMed1992

Structural changes in profilin accompany its binding to phosphatidylinositol, 4,5-bisphosphate.

The effect on the structure of profilin of phosphatidylinositol 4,5-bisphosphate (PIP2) binding was probed by fluorescence and circular dichroism (CD) spectroscopy. Fluorescence of Trp3 and Trp31 of profilin at 292 nm showed a linear decrease in solution emission at 340 nm as PIP2/profilin was increased from 0 to 80:1, apparently due to a static quenching mechanism involving formation of a nonfluorescent PIP2/profilin complex. CD spectra revealed an increase of up to 3.3-fold in the molar ellpticity at 222 nm for profilin as it binds PIP2, as well as changes in the Cotton effect between 250 and 310 nm. These results are consistent with a possible increase in the alpha-helix content of profilin triggered by the binding of PIP2.

Animals↗

PubMed1992

Characterization of tertiary interactions in a folded protein by NMR methods: studies of pH-induced structural changes in human growth hormone.

The pH-induced conformational changes in human growth hormone (hGH) have been studied, using a new quantitative NMR approach that combines 13C labeling of specific backbone carbonyl carbons with a complete spectral analysis of the corresponding 13C resonances. Thus, a complete analysis of the carbonyl resonances of the 26 Leu residues of hGH and their variation with pH provided detailed information about the equilibrium folding processes of the protein, including information about the kinetics of the folding. By combining this information with the pH dependence of readily identifiable 1H resonances, the pH-induced changes observed in the carbonyl carbon spectra can be associated with specific regions in the protein and can be ascribed to a series of localized adjustments in the tertiary structure, brought about by changes in the hydrogen bond interactions or electrostatic interactions between different residues in the globular folded protein. The preexchange lifetimes of these adjustments range from a fraction of a millisecond to a few milliseconds.

Amino Acid Sequence↗

PubMed2001

Structural changes of tRNA and 5S rRNA induced with magnesium and visualized with synchrotron mediated hydroxyl radical cleavage.

The structure of native yeast tRNA(Phe) and wheat germ ribosomal 5S RNA induced by different magnesium ion concentrations was studied in solution with a synchrotron mediated hydroxyl radical RNA cleavage reaction. We showed that very small amounts of Mg+2 can induce significant changes in the hydroxyl radical cleavage pattern of tRNA(Phe). It also turned out that a reactivity of tRNAz(Phe) towards *OH coincides with the strong metal binding sites. Because of the Mg ions are heavily hydrated one can suggest the strong correlation of the observed nucleosides reactivity in vicinity of Mg2+ binding sites with availability of water molecules as a source of hydroxyl radical. On the other hand the structure of wheat germ 5S rRNA is less sensitive to the hydroxyl radical reaction than tRNA(Phe) although some changes are visible at 4 mM Mg ions. It is probably due to the lack of strong Mg+2 binding sites in that molecule. The reactivity of nucleotides in loops C and D of 5S rRNA is not effected, what suggests their flexibility or involvement in higher order structure formation. There is different effect of magnesium on tRNA and 5S rRNA folding. We found that nucleotides forming strong binding sites for magnesium are very sensitive to X-ray generated hydroxyl radical and can be mapped with *OH. The results show, that guanine nucleotides are preferentially hydrated. X-ray footprinting mediated hydroxyl radical RNA cleavage is a very powerful method and has been applied to studies of stable RNAs for the first time.

Base Sequence↗

PubMed1997

Brain and erythrocyte anion transporter protein, band 3, as a marker for Alzheimer's disease: structural changes detected by electron microscopy, phosphorylation, and antibodies.

Band 3, a ubiquitous membrane transport, regulatory, and structural protein, is represented in brain by at least 4 isoforms. Bands 3 in brain performs the same functions as it does in erythrocytes (RBC). It is susceptible to oxidative damage, which, ultimately, terminates its life and that of the cell. We examined the changes band 3 undergoes in Alzheimer's disease (AD) because our previous studies suggest that band 3 is a pivotal protein in neurological disease. Because we hypothesize that AD is a total body disease, we examined peripheral blood cells as well as brain tissue to determine whether the same changes occur in both. Our results indicate that posttranslational changes occur in RBC band 3 that parallel changes in brain band 3. These include decreased 32P-phosphate labeling in vitro of band 3 polypeptides in brain and RBC, increased degradation of band 3, alteration in band 3 recognized by polyclonal and monoclonal antibodies, and decreased anion and glucose transport by blood cells. Serum autoantibodies to band 3 peptides 588-602 and 822-839 were increased in AD patients compared to controls. These band 3 residues lie in anion transport/binding regions. This is consistent with alteration of this region in AD since it is recognized as antigenically different by the patients' immune system. Our data support an immunological component to AD. The finding that changes in RBC in AD reflect those in brain and can be recognized by antibodies should facilitate development of blood tests for diagnosis and monitoring, and early therapy. It is anticipated that identification of molecular sites of posttranslational modification of band 3 will enable us to design specific preventive and treatment strategies, and target drugs to crucial molecular sites.

Aging↗

PubMed1984

Secondary structural changes in globular protein induced by a surfactant: Fourier self-deconvolution of FT-IR spectra.

Conformational changes in ovalbumin, a globular protein, induced by an anionic surfactant, sodium dodecyl sulfate (SDS), have been monitored by an FT-IR spectrometer using ZnSe cylindrical internal reflection optics which allows high quality IR spectra to be obtained in water solution. The most notable change, on addition of SDS, occurs in the composite band of the Amide I absorption band and the vibrational frequency of the composite C = O bond shifts from 1639 cm-1 to 1652 cm-1. On the other hand, the position of the Amide II band remains fairly unchanged. Comparison of the various peak positions in the deconvoluted spectra for the native protein and the perturbed protein clearly shows the effect of SDS on the secondary structures of the protein. SDS unfolds the protein. It increases the helix content slightly. More importantly, it alerts the beta sheet structure, destroying it almost completely in the Amide I region, while retaining it in its neighbourhood. In the deconvoluted spectra of the perturbed protein, a band at 1531 cm-1 indicates generation of some beta turns. We used the second derivative of the deconvoluted spectra for fixing positions of minor peaks and shoulders. The results of this study indicate that the deconvolution of the normal IR spectra, consisting of composite bands, provides evidence for the specific secondary structures in a protein and for the way they are affected by changes in the environment, e.g., the addition of SDS. This makes it possible to relate conformational changes to specific secondary structures.

Fourier Analysis↗

PubMed2005

Macrobenthos community structural changes off Cesenatico coast (Emilia Romagna, Northern Adriatic), a six-year monitoring programme.

Soft bottom macrobenthos at a station located off Cesenatico (Emilia Romagna, Northern Adriatic Sea) was investigated seasonally for six years from July 1996 to July 2002. Species composition and abundance of the community have been studied in relation to fluctuation in the water environment parameters, sediment texture patterns and mucilage, that occurred mainly in the water column at the study site. Three major Po river flow peaks occurred in November 1996, October 2000 and May 2002; after these events the community was reduced to minimum abundance values (total density<2000 individuals m(-2)). In the period between the first two episodes the river discharge remained rather low and conditions of increased salinity, lower nutrients and chl a and good oxygen saturation were experienced. The fossorial Crustacean Ampelisca diadema became dominant in the community between the first two river flow events, reaching maximum density of 10,200 individuals m(-2) and substituting the bivalve Corbula gibba, indicator of sediment instability. Species richness increased in the same period. The role of Ampelisca as a facilitator in structuring the community is discussed. Corbula gibba never recovered to initial densities, apart from an abundance peak that occurred in the summer of 2000. Faunal composition seemed to evolve slowly towards a higher degree of structural complexity (positive trend in diversity and evenness index). In the study site near-bottom mucilage events occurred in the summers of 1997, 1998, 2002; they appeared uncorrelated with the observed changes in the community structure. Multivariate analysis of community structure (MDS, ANOSIM) illustrates that community changes in this station are driven mainly by hydrographical conditions influencing sediment texture patterns and trophic resources for the benthos.

Animals↗

PubMed1998

Tertiary structural changes in the cleft containing the ATP sensitive tryptophan and reactive thiol are consistent with pivoting of the myosin heavy chain at Gly699.

The conformation of myosin subfragment 1 (S1) in the vicinity of the ATP sensitive tryptophan (Trp510) and the highly reactive thiol (SH1), both residing in the "probe-binding" cleft at the junction of the catalytic and lever arm domains, was studied to ascertain its role in the mechanism of energy transduction and force generation. In glycerinated muscle fibers in rigor, a fluorescent probe linked to SH1 detects a strained probe-binding cleft conformation following a length transient by altering emission intensity without detectably rotating. In myosin S1 in solution, the optical activity of Trp510 senses conformation change in the probe-binding cleft caused by substrate analog trapping of S1 in various structures attainable transiently during normal energy transduction. Also in S1 in solution, the induced optical activity of a fluorescein probe linked to SH1 shows sensitivity to changing probe-binding cleft conformation caused by nucleotide binding to the S1 active site. The changes in the optical activity of Trp510 and SH1 bound fluorescein in response to nucleotide or nucleotide analog binding are interpreted structurally using the S1 crystallographic coordinates and aided by a model of energy transduction that pivots at Gly699 to change probe-binding cleft conformation and to displace the S1 lever arm as during force generation. The crystallographic structure of the probe-binding cleft in S1 resembles most the nucleotide bound conformation in the native protein. A different structure, generated by pivoting at Gly699, better resembles the native rigor conformation of the probe-binding cleft. Pivoting at Gly699 rotates probes at SH1 suggesting that length transients on fibers in rigor do not cause pivoting at Gly699 or reverse the power stroke.

Adenosine Triphosphate↗

PubMed1988

Structural changes produced in Kupffer cells in the rat liver by injection of lipopolysaccharide.

The fine structure of Kupffer cells has been studied at various times after an intravenous injection of lipopolysaccharide of Salmonella abortus equii. The most prominent effects were: an increase in the number and dimensions of phagocytic vacuoles (often containing ingested LPS and neutrophilic granulocytes); mitochondrial damage, including disintegration of the matrix and cristae; an increase in the amount of dilated, lucent rough endoplasmic reticulum; presence of fat droplets in the cytoplasm. Five days after injection of lipopolysaccharide, the Kupffer cells had resumed their normal ultrastructure. Several minutes after injection of lipopolysaccharide, platelets adhered to the Kupffer and endothelial cells. Between one and six hours, neutrophilic granulocytes accumulated in the liver sinusoids. The resulting obstruction of the hepatic microcirculation most probably affected cellular ultrastructure by ischaemia. At three days, the number of Kupffer cells was doubled, and increased further at later time intervals.

Animals↗