Showing papers on "Circular dichroism published in 1980"
TL;DR: By including all types of secondary structure and by enlarging substantially the spectral region, the method permits analysis of the conformation of a variety of proteins, such as nucleic acid-binding proteins, immunoglobulins and β-pleated sheet-rich proteins.
751 citations
01 Jan 1980
TL;DR: This review focuses both on model peptides and biological activity polypeptide molecules and on intramolecularly hydrogen-bonded peptide structures involving a side-chain group, the N-protecting group, and a beta-amino acid.
Abstract: (1980). Intramolecularly Hydrogen-Bonded Peptide Conformation. Critical Reviews in Biochemistry: Vol. 9, No. 1, pp. 1-44.
343 citations
TL;DR: The data indicate that 7-S collagen is a unique component of basement membranes which shows a more compact and stable structure than other collageneous proteins.
Abstract: A new type of collageneous structure, tentatively named 7-S collagen, was isolated from a mouse tumor basement membrane, mouse and human placenta, bovine lens capsule and human kidney. The protein was solubilized from the tissues by limited digestion with pepsin or trypsin and could easily be separated from other collageneous protein because of its resistance towards further degradation by bacterial collagenase at 20 degrees C. 7-S collagen showed an amino acid composition typical of basement membrane collagen and contained 22% carbohydrate mainly as glucosyl-galactosyl bound to hydroxylysine but also some mannose and glucosamine. Ultracentrifugal analysis demonstrated that the proteins were homogeneous with a sedimentation coefficient of about 7.2 S and with a molecular weight of about 360,000 both in phosphate buffer pH 7 and 6 M guanidine. The peptide was triple helical as shown by circular dichroism and exhibited a biphasic melting profile indicating two conformationally distinct domains with tm = 48 degrees C and 70 degrees C. The more stable domain could be isolated as an homogeneous fragment (Mr = 225,000) after a second digestion with collagenase at 37 degrees C. This fragment contained all the disulfide bonds (42 Cys/1,000 residues) of the original molecule. Electron microscopy showed a rod-like structure in agreement with the hydrodynamic properties of 7-S collagen. The dimensions of these peptides were 3 X 95 nm (long form) and 2.4 X 40-50 nm (short form). Complete reduction of 7-S collagen under denaturing conditions produced several polypeptide chains in the molecular weight range of 27,000-153,000 which differ from each other by Mr increments 25,000-27,000. Separation of the chains on agarose did not reveal any simple stoichiometric relationship indicating that some chains are either cross-linked or represent fragments produced during proteolytic treatments. Complete reduction of 7-S collagen under non-denaturing conditions lowered the thermal transiton of the triple helix to 48 degrees C but did not change its molecular weight except when exposed to dissociating solvents. 7-S collagens were potent immunogens and could be characterized by radioimmunoassays. Antigenicity was slightly reduced by reduction and denaturation while collagenase at 37 degrees C produced a larger decrease. Proteins obtained from various sources showed distinct immunological relationships although interspecies differences in affinity exist. No or only little cross-reaction was observed with type IV and V collagens and some further fragments of basement membrane collagen. The data indicate that 7-S collagen is a unique component of basement membranes which shows a more compact and stable structure than other collageneous proteins.
291 citations
TL;DR: A model mechanism was devloped which quantitatively described the overall kinetics as well as the time course of the intermediates with a single set of parameters: the rate constant of cis leads to trans isomerization k = 0.015 s-1 and an average number of 30 tripeptide units in uninterrupted stretches of residues with all peptide bonds in trans configuration.
Abstract: The kinetics of triple-helix formation in type III pN-collagen, type III collagen and a quarter fragment of type III collagen was followed by optical rotation and circular dichroism. Kinetic intermediates were detected by trypsin digestion and polyacrylamide gel electrophoresis. The end products of refolding at 25 degrees C were identical to the native molecules according to their melting profiles, molecular weights and sedimentation behavior. Only at low temperatures (4-15 degrees C) were mismatched structures of lower stability formed. At 25 degrees C helix formation started exclusively at the set of three disulfide bridges which link the three chains at the carboxy-terminal end. The growth of the triple helix proceeds from this single nucleus at a rather uniform rate in a zipper-like fashion. This gives rise to zero-order kinetics over a large fraction of the conversion. Consequently the time of half conversion is proportional to the length of the molecule. From the appearance and disappearance of intermediates the growth of the triple helix could be observed directly. The rate of helix propagation is determined by the rate of cis leads to trans isomerization of peptide bonds. A model mechanism was devloped which quantitatively described the overall kinetics as well as the time course of the intermediates with a single set of parameters: the rate constant of cis leads to trans isomerization k = 0.015 s-1 and an average number of 30 tripeptide units in uninterrupted stretches of residues with all peptide bonds in trans configuration.
248 citations
TL;DR: In this paper, the pH dependence of warfarin binding to human serum albumin has been studied by circular dichroism, fluorescence, and equilibrium dialysis, showing that albumin complexes at low drug to protein ratios parallel the neutral to base transition, occurring in the protein over the pH range 6 to 9.
215 citations
TL;DR: The absorption spectrum of retinol when bound to β-lactoglobulin is vibrationally resolved and the circular dichroism spectrum exhibits the same structure, as does the fluorescence excitation spectrum.
207 citations
TL;DR: Interactions of aluminum with deoxyribonucleic acid (DNA) have been studied by thermal denaturation, circular dichroism, and fluorescent dye binding; a pH- and concentration-dependent alteration in the interaction of Aluminum with DNA was observed.
Abstract: Interactions of aluminum with deoxyribonucleic acid (DNA) have been studied by thermal denaturation, circular dichroism, and fluorescent dye binding; a pH- and concentration-dependent alteration in the interaction of aluminum with DNA was observed. Three distinguishable complexes are produced when DNA is denaturated at pH 5.0-7.5 and in aluminum to DNA mole ratios of 0-0.7. Complex I appears at neutral pH and stabilizes a portion of DNA. Complex II is observed at acidic pH, destabilizes a fraction of the DNA double-helical molecule, and produces intrastrand cross-links. Complex III occurs at all pHs, is maximal at intermediate pH values, and is characterized by a noncooperative melting profile and cross-linking at low pH (less than 6.0). The DNA in complexes II and III can be renatured by treatment with either ethylenediaminetetraacetic acid (EDTA) or a high concentration of sodium chloride. The properties of complexes I and II are consistent with what could be expected for DNA complexes of Al(OH)2+ and Al3+, respectively. Complex III has intermediate properties that are consistent with a structure in which both ions bind the DNA simultaneously. The characteristics of complex III depend on the ratio of Al3+/Al(OH)2+ in solution. Aluminum-DNA complexes differ from other metal-DNA complexes in that melting profiles under many conditions are biphasic. Apparently more than one form of DNA can exist at any time in the presence of aluminum. The different DNA-aluminum complexes, which arise from the multiple species of aluminum in aqueous solution, lead to a variety of reactions with DNA.
157 citations
TL;DR: The scope of circular dichroism in the characterisation of alginate composition and block-structure is assessed, and reliable estimates of composition can be obtained from the observed ratio of peak height to trough depth.
151 citations
TL;DR: This paper presents evidence for conformational transitions of the protein hormone induced by concentration and pH, and indicates that the hormone has two major conformational states: conformation I, a form which predominates in extremely dilute solutions and corresponds to the monomeric state, and conformation II, a forms present in the crystalline state.
Abstract: Conformational changes of bovine insulin in solution with concentration and pH detected by circular dichroic (CD) studies are reported. The change in the CD spectrum of insulin in the higher concentration range (from 100 microM down to 2 microM) is relatively small, but in the lower concentration range (from 2 microM down to 60 nM) the CD spectrum changes substantially with concentration. A detailed analysis of the data indicates that the hormone has two major conformational states: conformation I, a form which predominates in extremely dilute solutions and corresponds to the monomeric state, and conformation II, a form present in the crystalline state and also, with but minor changes, in all associated states in solution. The apparent conformation of insulin at various concentrations is computed by using a nonlinear least-squares iterative computer program. The mean residue ellipticities at 223 and 208 nm are extrapolated by using [theta] lambda VS. fmonomer plots to calculate the conformations of monomeric and dimeric insulin. These calculations indicate that conformation I of insulin has 21% less helix content than conformation II, the latter conformation being very similar to that found in the crystalline state. It is also evident from these calculations that the conformational transition is of the helix--coil type. Studies pertaining to the dependence of the CD spectrum of insulin on pH are also reported, and a comparison is made with earlier sedimentation coefficient studies. An analysis of the data indicates that changes in the sedimentation coefficient correspond quite closely to changes of CD spectra with pH. This paper is the first report known to us pertaining to conformational studies of insulin in the monomeric state; it presents evidence for conformational transitions of the protein hormone induced by concentration and pH. Since insulin is biologically active mainly in the monomeric state, a knowledge of its conformation in this state should be an important tool in deciphering the molecular basis of insulin action.
128 citations
01 Jan 1980
TL;DR: This review includes experimental and theoretical work on absorption and scattering of light by chiral macromolecules, and theoretical methods that relate the absorption and circular dichroism of a polymer or aggregate to the optical proper ties of its constituent parts.
Abstract: This review includes experimental and theoretical work on absorption and scattering of light by chiral macromolecules. All molecules absorb light, but only chiral (handed) molecules show a preferential absorption for right or left circularly polarized light. This phenomenon of circular dichroism (CD) has been very useful in characterizing any chiral aggre gate of chromophores-including proteins, nucleic acids, and their complexes. We discuss theoretical methods that relate the absorption and circular dichroism of a polymer or aggregate to the optical proper ties of its constituent parts. The experimental data reviewed is limited essentially to nucleic acids, for lack of space. Two new experimental methods that are particularly useful for mac romolecules or for systems that scatter a significant fraction of the incident light are fluorescence-detected circular dichroism and circular intensity differential scattered light. Fluorescence-detected circular di chroism (FDCD), as the name implies, used the intensity of the fluores cence emitted to monitor the intensity of the light absorbed (167). This method provides two main advantages: (a) The spectrum of a complex system containing many chromophores, but only a few fluorophores is greatly simplified, and (b) scattering artifacts, which plague circular dichroism studies using transmitted light measurements, are partly avoided by use of fluorescence detection. The theory (159, 160) and
118 citations
TL;DR: The results indicate that C8 is an atypical serum protein with regard to both its subunit structure and denaturation characteristics.
TL;DR: The amphipathic helix hypothesis for plasma lipoproteins was investigated using synthetic peptides and the findings support the earlier suggestions of the importance of the charged residues, but do not define the precise mechanisms involved.
TL;DR: Both the relatively high content of secondary structure in a peptide of this size and the conformational transition observed in changing from aqueous to nonpolar environments may reflect structural properties critical to the physiological function of NH2-terminal extension sequences, and both are consistent with current theories regarding the role of precursor regions in the intracellular transport and secretion of proteins.
Abstract: the secondary structure of a synthetic peptide representing the NH2-terminal, precursor-specific extension sequence of preproparathyroid hormone was studied. NH2-terminal extensions, or leader sequences, may serve a critical role in determining and facilitating the cellular secretion of proteins. These precursor regions, including the synthetic hormonal fragment studied, share common features of amino acid sequence and also may be similar in secondary structure. The secondary structure of the synthetic precursor peptide was predicted as described [Chou, P. Y. & Fasman, G. D. (1978) Adv. Enzymol. 47, 45-148]. The secondary structure was derived from circular dichroism spectra in both an aqueous buffer at physiological pH and in a nonpolar solvent selected to approximate the intramembranous environment. Two highly structured conformations were observed. In the aqueous buffer the secondary structure was 27% alpha-helix, 43% beta-sheet, and 30% random coil. In the nonpolar solvent the secondary structure was 46% alpha-helix, 0% beta-sheet, and 54% random coil. These findings correlated well with the two highest-probability structures predicted from the amino acid sequence. Both the relatively high content of secondary structure in a peptide of this size (30 amino acids) and the conformational transition observed in changing from aqueous to nonpolar environments may reflect structural properties critical to the physiological function of NH2-terminal extension sequences, and both are consistent with current theories regarding the role of precursor regions in the intracellular transport and secretion of proteins.
TL;DR: The results suggest a high degree of structural homology between the three enzymes and compare favorably to the X-ray-determined values of 41.6% helix and 25.8% β-strand for dogfish skeletal muscle lactate dehydrogenase.
TL;DR: It is proposed that the so-called psi-type CD spectrum is a manifestation of a side-by-side packing of DNA molecules with a long-range twisting order whose helical parameters match the helical parameter of circularly polarized light at specific resonance or critical wavelengths.
Abstract: The contribution of scattering to the circular dichroism (CD) of DNA films with twisted structures, DNA-polylysine complexes, and condensed DNA aggregates in ethanolic buffers of defined salt concentrations has been studied by the use of novel measuring techniques. These techniques include fluorscat cuvettes, fluorescence-detected circular dichroism (FDCD) methods, backscattering capturing devices, and beam-mounted goniometer detectors. The result of the experimental measurement is that DNA films can be made which have very large ellipticities or CD at sharp specific wavelengths. The sign of these ellipticities is related to the handedness of the twists, with a right-handed twist producing large positive rotations and a left-handed one producing negative rotations. The film shows nodal angles at which the interaction with light is minimal. The scattering patterns of both films, DNA-polylysine particles and DNA-EtOH condensates, show that the main interaction is light scattering produced by a resonance phenomenon similar to that produced in cholestric liquid crystals and twisted-nematic liquid crystals. It is proposed that the so-called psi-type CD spectrum is a manifestation of a side-by-side packing of DNA molecules with a long-range twisting order whose helical parameters match the helical parameter of circularly polarized light at specific resonance or critical wavelengths. Application of themore » Bragg law for cholesteric liquid crystals gives the periodicity of the long-range ordered structures. 9 figures.« less
TL;DR: Pectins of both high and low ester content form gels without the necessary involvement of divalent cations, at low pH and decreased water activity, presumably because these conditions minimize intermolecular electrostatic repulsion and promote chain~zhain rather than chain solvent interactions.
TL;DR: DNA fibers immersed in certain media clearly do adopt the C form based on their diffraction patterns, and several cases have a greater helical rotation per residue than those that had been noted previously by Marvin et al. (1961), and so extend the range of structures which may be termed C form.
TL;DR: A detection system for simultaneous monitoring of the light-obsorption (absorbance, A ) and the optical activity as circular dichroism (differential absorbance for left and right-circularly polarized light, Δ A A R ) of the eluent from a liquid-chromatograpy column is described in this article.
TL;DR: Polarized Fourier transform infrared spectroscopy and far ultraviolet circular dichroism of oriented multilamellar films of photoreceptor membranes indicate rhodopsin alpha-helices are predominantly oriented perpendicular to the bilayer plane.
TL;DR: It is suggested that the previously reported different electronic heme structures in the oxidized proteins are a consequence of the different mode of binding of the axial methionine.
TL;DR: In this paper, the first use of synchrotron radiation for circular dichroism (CD) measurements was described and the measurements were carried out in the wavelength range 1325-2050 A on (+)-3-methylcyclopentanone at the Synchrotrom Radiation Center of the University of Wisconsin-Madison.
TL;DR: In this article, the degree of alignment relative to a DNA fixed axis in this plane may be directly probed through the sign of the circular dichroism induced in an adduct transition of known polarization.
TL;DR: It is shown that the right-handed single helix of the trimer occurs in two distinct forms: the major one corresponds to a B-DNA-like structure, S-S-S; the minor one has the sugar rings in a hitherto unsuspected S- S-N conformational sequence.
Abstract: Proton NMR studies at 360 MHz were carried out on the trinucleoside diphosphate dApdApdA, the dinucleoside monophosphate dApdA and the methylphosphate esters of the monomers pdA, pdAp and dAp. The compounds were also investigated by means of circular dichroism at varying temperatures. Complete NMR spectral assignments are given. The thermodynamics of stacking derived from the circular dichroic spectra was used to extrapolate the observed coupling constants, measured at a range of temperatures, to values appropriate to the pure stacked states of the dimer and the trimer. The data were interpreted in terms of the N and S deoxyribose pseudorotational ranges [Altona, C. and Sundaralingam, M. (1972) J. Am. Chem. Soc. 94, 8205--8212] and it is shown that the right-handed single helix of the trimer occurs in two distinct forms: the major one corresponds to a B-DNA-like structure, S-S-S; the minor one (30%) has the sugar rings in a hitherto unsuspected S-S-N conformational sequence. The dimer behaves quite similarly, a mixture of 70% S-S and 30% S-N stacks being indicated. The detailed geometry of teh S-type sugar rings is not invariable but appears to undergo a slight shift when another base stacks on top of a given nucleotide unit. The backbone angles of the fully stacked B-DNA-like single helix in solution are (starting the notation at P) beta = 187 degrees, gamma = 50 degrees, delta = 138 degrees, epsilon = 186 degrees.
TL;DR: Using this highly homogeneous DNA, it is confirmed that the Pohl-Jovin transition is an intramolecular rearrangement, not requiring complete strand separation.
Abstract: We have studied the conformation of poly (dG-dC) . poly (dG-dC) in three conditions; i) associated with histones octamers, ii) alone at ionic strength 0.1, and ii) in solutions of over 2.5 M NaCl. The circular dichroism spectrum for the polymer bound to histones differs from that for the free polymer; the difference spectrum is similar to those for native and poly (dA-dT) . poly (dA-dT) core particles. Under the first two conditions, the 31P NMR spectrum is symmetric with line widths of 91 and 41 Hz, respectively, at 109.3 MHz. In high salt, two 31P peaks of equal intensity are observed, confirming recent results of Patel et al. (1) and indicating an alternating geometry for the phosphodiester backbone. Using this highly homogeneous DNA, we confirm that the Pohl-Jovin transition (2) is an intramolecular rearrangement, not requiring complete strand separation.
01 Sep 1980
TL;DR: The interaction of gramicidin A with lysolecithin micelles and with leCithin liposomes is demonstrated by circular dichroism to result in several metastable conformational states.
Abstract: The interaction of gramicidin A with lysolecithin micelles and with lecithin liposomes is demonstrated by circular dichroism to result in several metastable conformational states. A stable state can be obtained after extensive heating when the gramicidin A was added dry or in ethanol solution to the phospholipid dispersion but the stable state is readily obtained when gramicidin A is added in a trifluoroethanol solution. The circular dichroism of the stable conformational state is characterized by negative ellipticity below 205 nm and principally by a positive 220 nm band on which is superposed a weak 230 nm band (the latter likely arising from tryptophan side chains). The stable conformational state is considered to be that of the functional transmembrane channel primarily on the basis of extensive studies on its interaction with sodium ions.
TL;DR: The kinetics of unfolding and refolding of bovine carbonic anhydrase B by guanidinium chloride have been studied by simultaneously monitoring several spectroscopic parameters, each of which reflects certain unique conformational features of the protein molecule.
Abstract: The kinetics of unfolding and refolding of bovine carbonic anhydrase B by guanidinium chloride have been studied by simultaneously monitoring several spectroscopic parameters, each of which reflects certain unique conformational features of the protein molecule. In the present report, far-UV circular dichroism (CD) was used to follow the secondary structural change, UV difference absorption was used to follow the exposure or burying of aromatic amino acid residues, and near-UV CD was used to follow tertiary structural changes during unfolding and refolding. The unfolding is described by two unimolecular rate processes, and refolding is described by three unimolecular rate processes. The minimum number of conformational species involved in the mechanism is five. The refolding of the protein followed by the above three parameters indicates that the process consists of an initial rapid phase in which the random-coiled protein is converted to an intermediate state(s) having secondary structure comparable to that of the native protein. This is followed by the burying of the aromatic amino acid residues to form the interior of the protein molecule. Subsequently, the protein molecule acquires its tertiary structure and folds into a unique conformation with the formation of aromatic clusters.
TL;DR: A method is presented for determining the circular dichroism of systems whose CD spectra contain contributions from CD differential scattering, and it is asserted that these scattering patterns contain information about the tertiary structure of the condensed DNA particles studied.
Abstract: A method is presented for determining the circular dichroism (CD) of systems whose CD spectra contain contributions from CD differential scattering. The technique is shown to detect light over 4 pi steradians, and thus, for the first time, a complete correction for scattering is possible. The method is applied to ethanol-condensed DNA and poly[d(A-C).d(G-T)]. From the results obtained, the former are proposed to have an A-type secondary structure. The condensed polynucleotide particles are shown to exhibit behavior similar to that of cholesteric liquid crystals. CD difference spectra, obtained from the scattering corrections and showing the contributions to different sections of the scattering envelope, are displayed. It is asserted that these scattering patterns contain information about the tertiary structure of the condensed DNA particles studied.
TL;DR: The results lead to the apparent conclusion that, at least under these experimental conditions, the interactions between domains do not contribute greatly to the energetics of the folding process of the large β 2 protein.
TL;DR: In this article, the chemical characterization of horse liver alcohol dehydrogenase solubilized in isooctane via reverse micelles formed by the anionic surfactant di (2-ethylhexyl) sodium sulfosuccinate (AOT) and water (0.6 to 4% v/v) is presented.
Abstract: The chemical characterization of horse liver alcohol dehydrogenase solubilized in isooctane via reverse micelles formed by the anionic surfactant di (2-ethyl-hexyl) sodium sulfosuccinate (AOT) and water (0.6 to 4% v/v) is presented. The enzyme’s catalytic activity toward acetaldehyde reduction is markedly dependent upon w0 = [H2O]/[AOT], and upon the pH of the stock aqueous solution (pHst), from which the hydrocarbon enzyme solution is prepared. Kinetically, the micellar solution appears to follow a normal Michaelis-Menten behavior, with a turnover number which, under the optimal conditions (w0 = 42, pHst = 8.8), appears to be higher than in bulk water. The affinity between enzyme and NADH, as judged from direct binding studies (quenching of the protein fluorescence), is much reduced with respect to water if concentrations refer to the water pool of the micelles, and comparable to water if concentrations refer to the overall volume (hydrocarbon plus water pool). Also, the Km values are much higher if concentrations refer to the water pool. Ultraviolet absorption studies show that the aromatic chromophores are not significantly perturbed on going from a water solution to the micellar solution. The essentially aqueous environment of the protein in the reverse micelles is confirmed by fluoresence studies. Circular dichroism studies show that the enzyme’s conformation in the micelles is similar to that in water; however, under certain conditions, small but significant changes of the main chain folding seem to occur, which do not impair enzymatic activity. The spectroscopic properties of NADH in the hydrocarbon phase (fluorescence and circular dichroism) are also investigated. The potential of the LADH-NADH system for technical applications (oxidoreduction of lipophylic substrates) is discussed.