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At least 829 records · Page 46Linked to original sources
PubMed2001

Photochemically induced electron transfer (PET) catalyzed radical cyclization: a practical method for inducing structural changes in peptides by formation of cyclic amino acid derivatives.

A new radical cyclization reaction of unsaturated amino acid derivatives is presented. The reaction is induced by photoelectron transfer (PET) catalysis and proceeds, in comparison to commonly applied methods, under mild, nonoxidizing, and nontoxic conditions in neutral medium. This type of radical cyclization reaction can be used in peptide chemistry for inducing structural changes in peptides.

Amino Acids, Cyclic↗
PubMed2000

Observations of light-induced structural changes of retinal within rhodopsin.

Photo-isomerization of the 11-cis retinal chromophore activates the mammalian light-receptor rhodopsin, a representative member of a major superfamily of transmembrane G-protein-coupled receptor proteins (GPCRs) responsible for many cell signal communication pathways. Although low-resolution (5 A) electron microscopy studies confirm a seven transmembrane helix bundle as a principal structural component of rhodopsin, the structure of the retinal within this helical bundle is not known in detail. Such information is essential for any theoretical or functional understanding of one of the fastest occurring photoactivation processes in nature, as well as the general mechanism behind GPCR activation. Here we determine the three-dimensional structure of 11-cis retinal bound to bovine rhodopsin in the ground state at atomic level using a new high-resolution solid-state NMR method. Significant structural changes are observed in the retinal following activation by light to the photo-activated M(I) state of rhodopsin giving the all-trans isomer of the chromophore. These changes are linked directly to the activation of the receptor, providing an insight into the activation mechanism of this class of receptors at a molecular level.

Animals↗
PubMed2006

Structural changes of an octanethiol monolayer via hyperthermal rare-gas collisions.

In situ scanning tunneling microscopy is used to measure the effect of hyperthermal rare-gas bombardment on octanethiol self-assembled monolayers. Close-packed monolayers remain largely unchanged, even after repeated collisions with 0.4 eV argon and 1.3 eV xenon atoms. In contrast, gas-surface collisions do induce structural changes in the octanethiol film near defects, domain boundaries, and disordered regions, with relatively larger changes observed for xenon-atom bombardment.

Journal Article↗
PubMed1990

Radiographic study of structural changes in the temporomandibular joint after oblique sliding osteotomy: comparison between the extra-oral and intra-oral approaches.

Oblique sliding osteotomy of the mandibular rami was performed on 41 patients by either an intra-oral (21 patients) or extra-oral (20 patients) approach. The temporomandibular joints were radiographed preoperatively and then immediately and 18 months postoperatively. Signs of structural changes were recorded so as to compare the two approaches to osteotomy. The most common findings following the operation were signs of sclerosis and bone remodelling in 85% and 73% respectively of the two groups but these differences were not statistically significant.

Adolescent↗
PubMedDate not supplied

[Localization of minor proteins and structural changes in the myosin filaments of vertebrate striated muscle].

The origin of meridional reflections in the X-ray diffraction patterns of vertebrate skeletal muscles in resting and rigor states was studied. The main results may be summarized as follows. 1. Most of the meridional reflections localized in groups at the positions of successive orders of the repeat period of about 430 A are contributed mainly by the C-protein component of thick filaments. 2. The meridional reflections at about 143 and 72 A in the X-ray diffraction pattern of the resting muscle are contributed mainly by the cross-bridge axial repeat period, while in the X-ray diffraction patterns of the rigorized muscle the reflections at approximately the same positions are contributed mainly by C-protein. The change in the positions of these particular reflections accompanying the transition of the muscle from rest to rigor and from rest to contraction cannot be considered as an indication of a change in the axial repeat period of the cross-bridges, as it was earlier suggested by some authors. 3. The transition of the muscle from resting to rigor state is accompanied by substantial changes in the positions of the meridional reflections contributed my minor proteins, which is indicative of the structural transition in the thick filaments. The observed changes may be interpreted as the result of the thick filaments elongation by about 1.5% or, alternatively, as a consequence of the redistribution of electron density of the meridional reflections 215 and 143 A during a single twitch of the muscle (Huxley et al., Nature, 1980 284, 140) may be interpreted as a natural consequence of the structural change in the thick filaments. It is concluded therefore that on stimulation of the vertebrate skeletal muscle the thickness filaments undergo a reversible structural change which may reflect the existence of myosin-linked regulation in that type of muscle.

Animals↗
PubMed2002

A new electron transport mechanism in mitochondrial steroid hydroxylase systems based on structural changes upon the reduction of adrenodoxin.

The adrenal ferredoxin (adrenodoxin, Adx) is an acidic 14.4-kDa [2Fe-2S] ferredoxin that belongs to the vertebrate ferredoxin family. It is involved in the electron transfer from the flavoenzyme NADPH-adrenodoxin-reductase to cytochromes P-450(scc) and P-450(11)(beta). The interaction between the redox partners during electron transport has not yet been fully established. Determining the tertiary structure of an electron-transfer protein may be very helpful in understanding the transport mechanism. In the present work, we report a structural study on the oxidized and reduced forms of bovine adrenodoxin (bAdx) in solution using high-resolution NMR spectroscopy. The protein was produced in Escherichia coli and singly or doubly labeled with (15)N or (13)C/(15)N, respectively. Approximately 70 and 75% of the (15)N, (13)C, and (1)H resonances could be assigned for the reduced and the oxidized bAdx, respectively. The secondary and tertiary structures of the reduced and oxidized states were determined using NOE distance information. (1)H(N)-T(1) relaxation times of certain residues were used to obtain additional distance constraints to the [2Fe-2S] cluster. The results suggest that the solution structure of oxidized Adx is quite similar to the X-ray structure. However, structural changes occur upon reduction of the [2Fe-2S] cluster, as indicated by NMR measurements. It could be shown that these conformational changes, especially in the C-terminal region, cause the dissociation of the Adx dimer upon reduction. A new electron transport mechanism proceeding via a modified shuttle mechanism, with both monomers and dimers acting as electron carriers, is proposed.

Adrenodoxin↗
PubMed2001

HIV-1 nucleocapsid protein zinc finger structures induce tRNA(Lys,3) structural changes but are not critical for primer/template annealing.

Retroviral reverse transcriptases use host cellular tRNAs as primers to initiate reverse transcription. In the case of human immunodeficiency virus type 1 (HIV-1), the 3' 18 nucleotides of human tRNA(Lys,3) are annealed to a complementary sequence on the RNA genome known as the primer binding site (PBS). The HIV-1 nucleocapsid protein (NC) facilitates this annealing. To understand the structural changes that are induced upon NC binding to the tRNA alone, we employed a chemical probing method using the lanthanide metal terbium. At low concentrations of NC, the strong terbium cleavage observed in the core region of the tRNA is significantly attenuated. Thus, NC binding first results in disruption of the tRNA's metal binding pockets, including those that stabilize the D-TPsiC tertiary interaction. When NC concentrations approach the amount needed for complete primer/template annealing, NC further destabilizes the tRNA acceptor-TPsiC stem minihelix, as evidenced by increased terbium cleavage in this domain. A mutant form of NC (SSHS NC), which lacks the zinc finger structures, is able to anneal tRNA(Lys,3) efficiently to the PBS, and to destabilize the tRNA tertiary core, albeit less effectively than wild-type NC. This mutant form of NC does not affect cleavage significantly in the helical regions, even when bound at high concentrations. These results, as well as experiments conducted in the presence of polyLys, suggest that in the absence of the zinc finger structures, NC acts as a polycation, neutralizing the highly negative phosphodiester backbone. The presence of an effective multivalent cationic peptide is sufficient for efficient tRNA primer annealing to the PBS.

Amino Acid Sequence↗
PubMed2003

Circulating adhesion molecules and carotid artery structural changes in patients with noninsulin-dependent diabetes mellitus.

Hypertension and non insulin-dependent diabetes mellitus (NIDDM) are well-known risk factors for atherosclerotic disease. Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) may exert a relevant role in the pathogenesis of atherosclerosis; their prognostic relevance has been recently demonstrated. The aim of the study was to investigate possible inter-relation between circulating adhesion molecule levels, carotid artery structure and endothelial function in 15 patients with NIDDM, as well as in 15 patients with both NIDDM and essential hypertension (NIDDM+EH) compared with 15 normal subjects (NS) and 15 euglycaemic patients with EH, matched for age, sex and body weight. All subjects were submitted to a biopsy of the gluteal subcutaneous fat. Small arteries were dissected and mounted on a micromyograph, and the media-to-lumen (M/L) ratio was then calculated. Carotid artery structure was investigated by Doppler ultrasound. Endothelial function was evaluated by investigation of the flow-mediated dilatation (FMD) of the brachial artery. ICAM-1 and VCAM-1 plasma levels were measured by ELISA. ICAM-1 and VCAM-1 plasma levels were significantly greater and FMD smaller in EH, NIDDM and NIDDM+EH than in NS, but no difference was observed among the three pathological groups. Carotid artery structural changes were more pronounced in NIDDM+EH. No significant difference was observed among NIDDM, EH and NS. The M/L ratio of subcutaneous small resistance arteries was significantly greater in NIDDM+EH than in NIDDM or EH. NS had a smaller M/L ratio than the other groups. Significant correlations were observed between ICAM-1 plasma levels and indices of carotid artery structure in diabetic patients. However, the relations were close only in NIDDM+EH. In conclusion, our data suggest that NIDDM+EH may present more pronounced vascular structural alterations than NIDDM, and that adhesion molecules plasma levels are closely inter-related with carotid artery structural alterations, at least in NIDDM+EH, but not with M/L ratio of small resistance arteries.

Carotid Arteries↗
PubMed2002

Resonance Raman spectroscopy and quantum chemical calculations reveal structural changes in the active site of photoactive yellow protein.

Photoactive yellow protein (PYP) is a bacterial photoreceptor containing a 4-hydroxycinnamyl chromophore. Photoexcitation of PYP triggers a photocycle that involves at least two intermediate states: an early red-shifted PYP(L) intermediate and a long-lived blue-shifted PYP(M) intermediate. In this study, we have explored the active site structures of these intermediates by resonance Raman spectroscopy. Quantum chemical calculations based on a density functional theory are also performed to simulate the observed spectra. The obtained structure of the chromophore in PYP(L) has cis configuration and no hydrogen bond at the carbonyl oxygen. In PYP(M), the cis chromophore is protonated at the phenolic oxygen and forms the hydrogen bond at the carbonyl group. These results allow us to propose structural changes of the chromophore during the photocycle of PYP. The chromophore photoisomerizes from trans to cis configuration by flipping the carbonyl group to form PYP(L) with minimal perturbation of the tightly packed protein interior. Subsequent conversion to PYP(M) involves protonation on the phenolic oxygen, followed by rotation of the chromophore as a whole. This large motion of the chromophore is potentially correlated with the succeeding global conformational changes in the protein, which ultimately leads to transduction of a biological signal.

Bacterial Proteins↗
PubMed2003

Structural changes of hexamethylenetetramine and undecanedioic acid co-crystal (HMT-C11) as a function of the temperature.

HMT-C11 belongs to the family of adducts formed by the co-crystallization of N(4)(CH(2))(6) molecules (hexamethylenetetramine or HMT) and aliphatic dicarboxylic acids HOOC(CH(2))(n - 2)COOH with 5 </= n </= 13 (Cn). The adducts exhibit a layered structure in which the packing between HMT and Cn is determined by strong hydrogen bonds. The compounds in this family studied so far present thermotropic structural phase transitions and, depending on the chain length, disordered, twinned and modulated phases. The structure refinement of HMT-C11 based on X-ray diffraction experiments indicates three distinct phases from the melting point down to liquid nitrogen temperature: phase I is not crystalline; phase II is disordered (stacking fault) and its average structure is described in space group Bmmb; phase III is partially disordered and its symmetry is P2(1)/c. The systematic study of the structure evolution of phase III upon cooling revealed that the disorder has a dynamic character (anharmonicity). The main structural change observed from 293 K down to 93 K is the increase of the tilting angle of the C11 chains relative to the layer plane and the rotation of the HMT molecules. Both HMT and C11 behave like rigid bodies in the temperature range investigated. The quality of the refinements leads to a conclusive model for the O-H.N hydrogen bonds linking HMT and C11.

Journal Article↗
PubMed2001

Al(3+) and Zn(2+)-induced structural changes and localization in a fully-hydrated live eukaryotic cellular model.

This study combined techniques that did not require preparation protocols that were potentially harmful to the cell, making it possible to investigate cells at, or close to, their natural physiological state. We used the freshwater protozoon Chilomonas paramecium as a eukaryotic cellular model to locate sites of Al(3+) or Zn(2+) accumulation and quantify the associated structural changes. Cells were fully hydrated throughout the study, which used a combination of differential interference contrast light microscopy, confocal laser scanning microscopy and transmission X-ray microscopy. The latter technique allowed high resolution (50 nm) and high contrast imaging of live cells in solution. For confocal laser scanning microscopy the relatively new fluorochrome Newport Green was used. This made fluorescent complexes with intracellular Al(3+) and Zn(2+), allowing localisation of metal-containing granules and vesicles. After long term exposure a previously unreported annular-shaped site of metal accumulation was found, signifying a vesicle with metal accumulated in the periphery only. After exposure to Al(3+) and Zn(2+), the cell pellicle was thinner and the majority of rounded-up cells had a concentric layering of organelles. By combining a variety of techniques it was possible to gain high resolution structural and chemical information on cells minimally exposed to potentially artefact-inducing procedures.

Aluminum↗
PubMed1986

Fatigue and structural change: two consequences of visual pattern adaptation.

In a tilt aftereffect (TAE) paradigm, 2 min of adaptation produced an aftereffect that decayed almost completely within 4 min. Four minutes of adaptation produced a TAE that lasted more than 2 wk. Two modes of adaptation contribute to the TAE and account for other aftereffects: short-term fatigue, produced very quickly and long-term structural change, requiring more extended adaptation.

Adaptation, Ocular↗
PubMed2006

SRC tail phosphorylation is limited by structural changes in the regulatory tyrosine kinase Csk.

Src family tyrosine kinases are down-regulated through phosphorylation of a single C-terminal tyrosine by the nonreceptor tyrosine kinase Csk. Despite the fundamental role of Csk in controlling cell growth and differentiation, it is unclear what limits this key signaling reaction and controls the production of catalytically repressed Src. To investigate this issue, stopped-flow fluorescence experiments were performed to determine which steps modulate catalysis. Both Src binding and phosphorylation can be monitored by changes in intrinsic tryptophan fluorescence. Association kinetics are biphasic with the initial phase corresponding to the bimolecular interaction of both proteins and the second phase representing a slow conformational change that coincides with the rate of maximum turnover. The kinetic transients for the phosphorylation reaction are also biphasic with the initial phase corresponding to the rapid phosphorylation and the release of phospho-Src. These data, along with equilibrium sedimentation and product inhibition experiments, suggest that steps involving Src association, phosphorylation, and product release are fast and that a structural change in Csk participates in limiting the catalytic cycle.

CSK Tyrosine-Protein Kinase↗
PubMed1984

[Structural changes in the contractile proteins of muscle fiber studied by polarization ultraviolet fluorescence microscopy. VII. The effect of Ca2+ on the nature of the conformational changes in F-actin induced by the binding of heavy meromyosin].

Changes in anisotropy of tryptophan fluorescence and in birefringence of actin filaments induced by the binding to actin of heavy meromyosin (HMM), both containing DTNB light chains and devoid of them, were found in rabbit muscle fibres free of myosin, troponin, and tropomyosin. Ca2+ was shown to affect the pattern of changes in tryptophan fluorescence anisotropy and birefringence of actin filament at the moment of HMM interaction with actin, providing HMM contains DTNB light chains. Anisotropy of tryptophan fluorescence and birefringence of actin filaments rises in the absence of Ca2+ (pCa greater than or equal to 7), while in its presence (pCa less than or equal to 6) these values drop down. Furthermore, these changes become cooperative when Ca2+ concentration increases from pCa = 7 to pCa = 6. It was shown that the binding of HMM devoid of DTNB light chains to F-actin decreases tryptophan fluorescence anisotropy and birefrigence of actin filaments, regardless of Ca2+ concentration. Ca2+-dependent structural changes of F-actin induced by interaction of heads of myosin molecules with actin are assumed to be of great importance in regulation of muscle contraction of vertebrate skeletal muscles.

Actins↗
PubMed2005

Light-induced structural changes of apoprotein and chromophore in the sensor of blue light using FAD (BLUF) domain of AppA for a signaling state.

AppA is a new class blue-light receptor controlling photosynthesis gene expression in the purple bacterium Rhodobacter sphaeroides and retains a characteristic flavin adenine dinucleotide (FAD)-binding domain named the "sensor of blue light using FAD" (BLUF). AppA functions as an antirepressor controlling transcription of photosynthesis genes through the direct association with a transcriptional repressor PpsR in a blue-light-dependent manner [Masuda and Bauer (2002) Cell 110, 613-623]. Illumination of AppA induces a red shift in the UV-visible absorption of FAD, which results in a signaling state of AppA. Light-induced Fourier transform infrared (FTIR) difference spectrum of the AppA BLUF domain showed relatively simple features, which were mainly composed of two sets of derivative-shaped sharp bands at 1709(-)/1695(+) and 1632(+)/1619(-) cm(-)(1). We have developed an in vitro reconstitution method, by which a fully functional BLUF domain was reconstituted from free FAD and an apoprotein for the BLUF domain of AppA. An AppA BLUF domain that consisted of an apoprotein isotopically labeled with (13)C and unlabeled FAD was constituted using this method, and hydrated and deuterated samples were applied to FTIR spectroscopic analyses. When the spectra for the reconstituted domain were compared with those for uniformly (15)N- and (13)C-labeled or deuterated domains as well as for the unlabeled domain, the IR bands responsible for the light-induced changes in the FAD chromophore and apoprotein were identified. Unexpectedly, the light-induced spectrum of the unlabeled BLUF domain of AppA was predominantly composed of multiple apoprotein bands, while a C(4)=O stretching of an isoalloxazine ring was the only band exclusively assigned to FAD. The results showed that relatively large structural changes occur in the protein backbone of the BLUF domain of AppA upon illumination. These changes were discussed in relation to the mechanistic role of the BLUF domain in the process of blue-light perception by AppA.

Apoproteins↗
PubMedDate not supplied

Airway inflammation and structural changes in airway hyper-responsiveness and asthma: an overview.

Asthma treatment has moved from bronchodilator therapy to an emphasis on anti-inflammatory therapy. Airway inflammation is believed to induce airway hyper-responsiveness (AHR) through the release of mediators that increase the airway response to agonists. However, the exact contribution of airway inflammation in the physiology of airway hyper-responsiveness remains undefined. Structural modifications in airways resulting from inflammation may contribute to the development and persistence of AHR and the development of asthma. This paper reviews some of the main components of airway inflammation and structural changes in asthma, and discusses how these processes may interact to modify airway function and induce respiratory symptoms.

Airway Resistance↗
PubMed2000

Long-term administration of D-NAME induces hemodynamic and structural changes in the cardiovascular system.

N(G)-nitro-D-arginine-methyl ester (D-NAME) is considered to be an inactive enantiomer of L-NAME and is generally used as the negative control for NO synthase inhibition with L-NAME. With the aim to compare the effects of 4-week L-NAME and D-NAME treatments on hemodynamic and cardiovascular structural parameters, four groups of male Wistar rats were investigated: the controls and groups administered 40 and 20 mg/kg/day of L-NAME and 40 mg/kg/day of D-NAME. At the end of the experiment, myocardial NO synthase activity decreased by 42, 24 and 25%; aortic NO synthase activity decreased by 35, 15 and 13% vs. controls in the L-NAME 40, L-NAME 20 and D-NAME 40 groups, respectively. The DNA concentrations in the myocardium and the aorta increased significantly after L-NAME and D-NAME treatments. The inhibition of NO synthase was accompanied by a significant elevation in systolic blood pressure in all three groups. The LVW/BW ratio increased by 27, 14 and 13% vs. controls in the L-NAME 40, L-NAME 20 and D-NAME 40 groups, respectively. The aortic wall mass, measured as the cross-sectional area, increased by 45, 17 and 25% vs. controls in the L-NAME 40, L-NAME 20 and D-NAME 40 groups, respectively. Myocardial fibrosis represented 0.94% in the controls, but 7.96, 4.70 and 5.25% in L-NAME 40, L-NAME 20 and D-NAME 40 groups, respectively. It is concluded that D-NAME, although less affective than L-NAME, inhibits NO synthase activity resulting in hemodynamic and structural changes in the cardiovascular system similar to the changes induced by half the dose of L-NAME. Thus, the consideration of D-NAME as an inactive enantiomer and its use as the negative control needs to be reevaluated.

Animals↗