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At least 235 records · Page 13Linked to original sources
PubMed1993

Fourier transform infrared difference spectroscopy of the nicotinic acetylcholine receptor: evidence for specific protein structural changes upon desensitization.

We have previously reported a new method based on Fourier transform infrared spectroscopy for probing conformational changes that occur upon the binding of ligands to the nicotinic acetylcholine receptor (nAChR) [Baenziger, J. E., Miller, K. W. & Rothschild, K. J. (1992) Biophys. J. 61, 983-992; Baenziger, J. E., Miller, K. W., McCarthy, M. P. & Rothschild, K. J. (1992) Biophys. J. 62, 64-66]. Spectra are recorded using attenuated total reflection both in the presence and absence of agonists. The resulting nAChR "resting-to-desensitized" difference spectra reveal small highly reproducible infrared bands which can arise from vibrations of the agonist and structural changes in the nAChR membrane during the conversion of the receptor from the resting to desensitized state. In this work we have used a combination of different agonists and an antagonist along with isotopic labeling to assign bands in these spectra. nAChR membranes pretreated with the competitive antagonist alpha-bungarotoxin exhibit no bands above the noise level (approximately 10(-5) au) demonstrating that vibrations of the unbound agonist do not contribute to the normal difference spectrum. In contrast, bands in the resting-to-desensitized difference spectra are identified which can be assigned to the bound agonist, providing a means to probe its interaction and orientation in the binding site. Additional difference bands are due to secondary structural changes of the protein, perturbation of tyrosine(s), and changes in carboxyl groups possibly from Asp and/or Glu residues. Remarkably, some of these spectral changes are similar to those detected during the bleaching of the photoreceptor membrane protein rhodopsin.

Animals↗
PubMed1997

Structural changes in insulin-like growth factor (IGF) I mutant proteins affecting binding kinetic rates to IGF binding protein 1 and IGF-I receptor.

Ligand binding properties of five single amino acid substituted variants (V11A, D12A, Q15A, Q15E, and F16A) of human insulin-like growth factor I (IGF-I) were analyzed with respect to their binding affinities and binding kinetics to recombinant IGF binding protein 1 (IGFBP-1) and a soluble form of the IGF type I receptor (sIGF-I(R)), respectively. Side chains of the substituted residues are all predicted to be the most surface exposed in the alpha-helical portion of the B-region of the IGF-I molecule. The IGF-I variants were produced as fusion proteins to a IgG(Fc) binding protein domain, Z. Ligand binding kinetic rates were determined using BIAcore biosensor interaction analysis technology. All IGF-I variants showed altered binding affinities to both IGFBP- I and sIGF-I(R). Secondary structure content of the IGF-I variants was estimated using far-UV circular dichroism spectroscopy, followed by variable selection secondary structure calculations. The amount of calculated alpha-helicity is reduced for all the mutants, most predominantly for IGF-I(V11A) and IGF-I(F16A) proteins. Surprisingly, most of the effects of reduced binding affinities to both target proteins are attributed to lowered on-rates of binding, and these are correlated with the amount of alpha-helicity in each IGF-I variant. In addition, in some of the IGF-I variants, lowered off-rates of binding are observed. From the results, we propose that IGF-I is unusually sensitive to structural changes by surface amino acid substitutions in the B-region of the molecule. Therefore, biochemical or biological properties of amino acid substituted variants of IGF-I cannot be used in a straightforward way to dissect the direct involvement in binding of individual amino acid residues since structural changes may be involved.

Amino Acid Sequence↗
PubMed1996

Structural changes in the intramuscular connective tissue during development of bovine semitendinosus muscle.

Structural changes in the intramuscular connective tissue during development of bovine semitendinosus muscle were investigated using the cell-maceration method for scanning electron microscopy, by which cellular elements were eliminated and collagen fibrils and fibres were exposed. The endomysium was discontinuous and showed various shapes and sizes in the muscle of 7-month fetuses. The perimysium consisted of collagen fibres in loose contact with each other. In the muscle of neonatal calves, the endomysium consisted of cylindrical sheaths and displayed a honeycomb structure, and the perimysium was composed of several layers of collagen fibres. Collagen fibrils in the endomysium bound ever more closely with each other, and collagen fibres in the perimysium increased in thickness, and the wavy pattern of collagen fibres became more regular with growth of cattle. We have examined the mechanical strength of the intramuscular connective tissue by our new method, 'intramuscular connective tissue (IMCT) model'. The IMCT model is composed of collagen fibrils and fibres which maintains the organization in the endomysium and perimysium in situ. The shear-force value of the model increased rapidly from the 7th fetal month to the neonatal stage, and increased linearly with postnatal ageing thereafter. Changes in the arrangement of collagen fibrils and fibres seem to closely related to an increase in the mechanical strength of the intramuscular connective tissue during development of bovine skeletal muscle.

Animals↗
PubMed1995

Structural changes in the water-oxidizing complex monitored via the pH dependence of the reduction rate of redox state S1 by hydrazine and hydroxylamine in isolated spinach thylakoids.

A detailed kinetic analysis is presented for the pH dependence of the reduction of the water-oxidizing complex (WOC) in redox state S1 by hydrophilic amines NH2R (R = NH2, OH) in suspensions of isolated thylakoids. Measurements of patterns of the oxygen yield induced by a train of single-turnover flashes and evaluation of the data within the framework of an extended Kok model [Messinger, J., Wacker, U., & Renger, G. (1991) Biochemistry 30, 7852-7862] led to the following results: (a) the rate constants kS1(NH2R) exhibit strikingly similar pH dependencies for NH2OH and NH2NH2 with "titration waves" at pH 5.3-5.6; 6.2-6.5, and above a critical pH value of about 7.4; (b) the differences in the reaction mechanism between NH2OH (1-electron reduction) and NH2NH2 (2-electron reduction) are almost pH-independent; (c) the ratio of the rate constants, kS1(NH2OH)/kS1(NH2NH2), decreases by a factor of about 9 within the range 5 < pH < 8.5. A detailed analysis reveals that these data cannot be consistently explained by the assumption that the unprotonated forms NH2OH and NH2NH2 are the active species while the protonated cations [NH3OH]+ and [N2H5]+ are nonreactive. A quantitative description is achieved by the additional postulate that pH-dependent structural changes take place in the WOC, thereby modulating the reactivity toward exogenous redox active amines of the type NH2R. On the basis of the results of this study and a recent report [Messinger, J., & Renger, G. (1994) Biochemistry 33, 10896-10905], it is inferred that the WOC undergoes three specific structural changes, with characteristic pH values of 5.3-5.5, 6.2-6.5, and above 7.4.

Hydrazines↗
PubMed1996

Structural change in alpha-chymotrypsin induced by complexation with alpha 1-antichymotrypsin as seen by enhanced sensitivity to proteolysis.

Both human neutrophil elastase (HNE) and free chymotrypsin (Chtr) proteolyze Chtr within the complex that Chtr forms with antichymotrypsin (ACT). As free Chtr is stable both to self-digestion and to digestion by HNE, these results are indicative of a stability and/or conformational change in Chtr that accompanies complex formation. As determined by both N-terminal sequence analysis and matrix-assisted laser desorption ionization mass spectroscopy (MALDI-MS), the major initial sites of HNE cleavage of complexed Chtr are between gamma-chain residues A158/S159 and V188/S189. Significantly, this latter site is at the base of the S1 site that recognizes the P1 position of the serpin. A slower cleavage in the beta-chain between T139/G140 is also found. In addition, rACT is cleaved between residues V22/D23. The gamma-chain of complexed Chtr is also cleaved by free Chtr, but at different sites: L162/L163 and W172/G173. beta-Chain cleavages were also found between residues Q81/K82 and F114/S115. Cleavages similar to those described above were also found when Chtr was complexed with the L358F-rACT variant, but not for Chtr complexed with either of the smaller inhibitors bovine pancreatic trypsin inhibitor or turkey ovomucoid third domain, nor for the covalent adduct of Chtr with N-p-tosylphenylalanyl chloromethyl ketone. We conclude that the structural change in Chtr making it a proteinase substrate is coupled with the large conformational change in ACT following complex formation. Complexed Chtr is much less reactive toward proteolytic digestion in the presence of high salt than in its absence, in accord with the high-salt induced release of active enzyme from the Chtr.rACT complex and the suggestion that electrostatic interactions mediate the coupling of structural change between rACT and Chtr within the Chtr.rACT complex. Potential physiological consequences of this work are explored.

Amino Acid Sequence↗
PubMed1981

Structural changes after transmitter release at the frog neuromuscular junction.

The sequence of structural changes that occur during synaptic vesicle exocytosis was studied by quick-freezing muscles at different intervals after stimulating their nerves, in the presence of 4-aminopyridine to increase the number of transmitter quanta released by each stimulus. Vesicle openings began to appear at the active zones of the intramuscular nerves within 3-4 ms after a single stimulus. The concentration of these openings peaked at 5-6 ms, and then declined to zero 50-100 ms late. At the later times, vesicle openings tended to be larger. Left behind at the active zones, after the vesicle openings disappeared, were clusters of large intramembrane particles. The larger particles in these clusters were the same size as intramembrane particles in undischarged vesicles, and were slightly larger than the particles which form the rows delineating active zones. Because previous tracer work had shown that new vesicles do not pinch off from the plasma membrane at these early times, we concluded that the particle clusters originate from membranes of discharged vesicles which collapse into the plasmalemma after exocytosis. The rate of vesicle collapse appeared to be variable because different stages occurred simultaneously at most times after stimulation; this asynchrony was taken to indicate that the collapse of each exocytotic vesicle is slowed by previous nearby collapses. The ultimate fate of synaptic vesicle membrane after collapse appeared to be coalescence with the plasma membrane, as the clusters of particles gradually dispersed into surrounding areas during the first second after a stimulus. The membrane retrieval and recycling that reverse this exocytotic sequence have a slower onset, as has been described in previous reports.

Animals↗
PubMed1988

Cardiovascular structural changes induced by isolation-stress hypertension in the rat.

The cardiovascular structural remodelling associated with psychogenic hypertension was investigated in genetically normotensive rats subjected to isolation stress. Male Wistar rats were stressed by intermittent social isolation and compared to control rats living in groups. The stressed rats had higher systolic blood pressures than the control rats throughout the study. After 1 week of isolation, ornithine decarboxylase activity, a marker for hypertrophy, was increased in the right ventricle of the stressed rats. After 6 weeks of intermittent isolation, the myocardium of the stressed rats was hypertrophied, involving both right and left ventricles. The aorta was also hypertrophied, whereas the tail artery remained unaffected. Later, after 12 weeks of isolation, the left ventricular hypertrophy persisted whereas the right ventricle and aorta returned to normal. It seems, therefore, that social stress hypertension is accompanied by very early structural changes, which affect at least the heart and the aorta, and cannot be directly linked to the severity or duration of hypertension.

Animals↗
PubMed1989

[Structural changes of the heart in craniocerebral trauma].

A study is presented of structural changes in the myocardium due to head injuries. General histological, histochemical, histoenzymological methods and electron microscopy were used. The authors revealed a complex of dystrophic and adaptative changes in the contractile myocardium, interstitial connective tissue and blood circulatory bed. These changes depended directly on the character of the craniocerebral injury and time from the beginning of the trauma.

Brain Injuries↗
PubMed1986

[Structural changes in the sugar chains of gamma-glutamyltranspeptidase by malignant transformation].

Structures of the sugar moieties of gamma-glutamyl transpeptidases purified from the kidney and the liver of rat, mouse, and cattle were studied after being chemically released as oligosaccharides. The results indicated that both organ-specific and species-specific differences exist in the sugar chains of the enzyme. Comparative studies of sugar chains of the heavy and light subunits of the rat kidney enzyme revealed that high mannose-type sugar chains are found only in the heavy subunit. By the same analysis of the oligosaccharide fractions obtained from four isozymic forms of the rat kidney enzyme, it was found that all these enzymes contain 2 mole of neutral sugar chains but different numbers of acidic sugar chains in one molecule. Comparative studies of oligosaccharides obtained from the enzymes purified from rat AH-66 hepatoma and from normal rat liver revealed that more than 40% of the sugar chains of the hepatoma enzyme contain bisecting N-acetylglucosamine residues which are not found in those of the liver enzyme. By making use of the structural changes associated with malignant transformation, a new diagnostic method or hepatoma was developed. In principle, the method consists of affinity chromatography of the desialylated serum enzyme using an erythroagglutinating lectin agarose column.

Animals↗
PubMedDate not supplied

[The role of structural changes in T4 bacteriophage tail proteins].

Conformational changes in bacteriophage tail proteins after heating and ionic strength alteration leading to dissociation of tail sheath have been studied using protein fluorescence, differential scanning microcalorimetry and electron microscopy methods. Autonomous structural changes in tube-baseplate proteins have been revealed. They take place under the same conditions as those which release the bonds holding the sheath protein subunits to those of the tube in isolated sheathed tails. The conformational changes in the tube-baseplates are reversible similarly to the process of assembly and disassembly of the extended sheath. Morphological changes in the tube have been found at the temperature above the transition registered by protein fluorescence but not by calorimetry. This suggests that revealed spectral alterations reflect changes in quaternary structure of tail tube in particular.

Calorimetry, Differential Scanning↗
PubMed1991

Target-dependent structural changes in sensory neurons of Aplysia accompany long-term heterosynaptic inhibition.

FMRFamide evokes both short-term and long-term inhibition of synapses between mechanosensory and motor neurons in Aplysia. We report here, using dissociated cell culture and low-light epifluorescence video microscopy, that depression lasting 24 hr of sensorimotor synapses evoked by four brief applications of FMRFamide is accompanied by a significant loss of sensory cell varicosities and neurites. These structural changes in the sensory cells require the presence of the target motor cell L7. Because the loss of structures known to contain transmitter release sites correlates significantly with the changes in the amplitude of the excitatory postsynaptic potential in L7, our results suggest that the structural changes evoked by FMRFamide reflect a loss of synaptic contacts. Thus, long-term depression parallels long-term facilitation of the sensorimotor synapse produced by serotonin in that both forms of heterosynaptic plasticity involve target-dependent modulation of the number of presynaptic varicosities.

Animals↗
PubMed1989

Calcium ion concentration detected by structural changes of a Millipore DOPH artificial membrane.

The surface structure of an artificial membrane composed of a Millipore filter and a synthetic lipid analogue, dioleylphosphate (DOPH), immersed in KCl solution changes when the CaCl2 concentration reaches a critical value. Using a photomultiplier mounted on the eyepiece of a stereoscopic microscope the structural change can be measured quantitatively as an intensity variation of reflected light of the membrane surface. Calcium ions decreased the intensity to about 50% of the original hydrophilic state whose solution was only KCl. However, the degree of structure change was dependent on adsorbed DOPH density, solution temperature and pH value. On the other hand, using the light reflectance curves obtained from the structural observations, an unknown CaCl2 concentration in a KCl solution can be determined. Since the reflectance curve shifts widely with various densities of DOPH adsorbed in the Millipore filter, it is possible to measure the CaCl2 concentration over a wide range. The detection range was from 0.1 to 50 mM CaCl2.

Adsorption↗
PubMed1982

Oxygen transfer, gill resistance and structural changes in rainbow trout (Salmo gairdneri, Richardson) gills perfused with vasoactive agents.

1. Gill resistance (Rg) and oxygen transfer (To2) were measured in perfused rainbow trout gills. After perfusion the gills were analysed morphometrically. 2. Rg increased with 40% and To2 decreased with 91% during 60 min perfusion without vasoactive substances in the perfusion Ringer. 3. In presence of 10 micro M adrenaline both Rg and To2 remained stable at their starting levels throughout the experimental period (60 min). 4. With 0.2 micro M acetylcholine and 10 micro M adrenaline in Ringer Rg increased nearby to the same extent as in perfusions without vasoactive agents, while To2 was not significantly affected. 1 micro M acetylcholine increased Rg with 76% and decreased To2 with 51%. 5. The changes in Rg and To2 could be explained by structural changes in the secondary lamellae.

Acetylcholine↗
PubMed1995

NMR spectroscopic characterization of adinazolam mesylate: pH-dependent structure change in aqueous solution and active methylene.

The present study is to investigate structural changes of adinazolam mesylate in aqueous solution under various pH conditions by NMR spectroscopy. By plotting of the signal integration and chemical shifts of the side chain, pKa values for imine hydrolysis and the side chain amine were determined. Conformational analysis of the side chain was performed with deuterium-induced isotope effects on chemical shifts, nuclear Overhauser effects, relaxation times, and energy calculations. Hydrogen/deuterium exchange due to an active methylene at the 4-position under basic conditions was revealed.

Antidepressive Agents↗
PubMed1993

Evaluation of structural change in diffuse liver disease with frequency domain analysis of ultrasound.

To evaluate structural changes in diffuse liver disease, frequency domain analysis was applied to ultrasonic signals from the liver. We assumed that liver tissue is a collection of semiregularly arrayed small scatterers of ultrasound. We applied cepstral analysis to the ultrasonic waveforms and evaluated the periodicity of scalloping of the power spectrum caused by an interference effect among liver scatterers of a given spacing. Patients with liver conditions involving nonspecific change (n = 6), chronic hepatitis (n = 11), cirrhosis (n = 7) or fatty liver (n = 6) were examined. One hundred ultrasonic signals were obtained noninvasively with a 3.5-MHz transducer, and the space among scatterers was calculated for each signal using cepstrum analysis. Two statistical parameters, mode and kurtosis, were determined from the distribution of the space among scatterers for each patient; these parameters were compared with the histological findings in the liver. Space among scatterers kurtosis decreased with progress of liver fibrosis, and space among scatterers mode increased in cirrhosis. Neither space among scatterers kurtosis nor space among scatterers mode was affected by pathological fat in the liver. These results suggest that we can evaluate fibrotic changes in diffuse liver disease and that we can also noninvasively discriminate diffuse fibrotic liver disease from fatty liver.

Chronic Disease↗
PubMed1986

[Structural changes in erythrocyte membranes during cooling studied by a spin probe method].

Peculiarities of structural changes in erythrocyte membranes during freezing (from -20 degrees to -50 degrees) were studied by electron paramagnetic resonance method using spin-labelled derivative of stearic acid-5-doxylstearate. It was established that membranes underwent a number of structural reconstructions due to the temperature decrease and water freezing-out. Differences were found in temperature dependences that characterize lipid ordering during probe insertion into membranes of native erythrocytes, white ghosts, and liposomes from total lipids of erythrocyte membranes. The data obtained indicate the impairment in the structure of lipid components and lipid-protein interactions in erythrocyte membranes during cooling.

Cold Temperature↗
PubMed1983

Fine structural changes in cat L7 ventral horn neurones after chronic sub LD50 DFP.

The fine structural changes in the ventral anterior horn of spinal segment L7, have been studied in adult cats after single and chronic sub LD50 (0.1 to 0.75 mg/kg SC with a cumulative range of 1.3 mg/kg to 10.5 mg/kg) low dose exposure to diisopropylfluorophosphate (DFP). Only the motoneurons of the chronically treated animals show an increase in the number of lysosomes, neurofilaments and vesicle-like structures. A large number of coated vesicles is observed within axons and axon terminals of both acute and chronically treated animals. Morphological evidence of axon and terminal degeneration is seen only in chronically treated animals. The present study shows that chronic sub LD50 low dose administration of DFP over periods from 5 to 21 days results in degenerative changes of presynaptic terminals and axons, with the severity of the changes being dependent on dose and duration of treatment. The data are interpreted by comparison with single high dose exposure reported in the literature with a discussion of acute and delayed neurotoxic effects of DFP, on the central nervous system.

Animals↗