bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature dependence and resonance assignment of 13C NMR spectra of selectively and uniformly labeled fusion peptides associated with membranes
Authors: Bodner Michele L. , Gabrys Charles M. , Parkanzky Paul D. , Yang Jun , Duskin Craig A. , Weliky David P. 
Published: January 2004

AbstractHIV‐1 and influenza viral fusion peptides are biologically relevant model fusion systems and, in this study, their membrane‐associated structures were probed by solid‐state NMR 13C chemical shift measurements. The influenza peptide IFP‐L2CF3N contained a 13C carbonyl label at Leu‐2 and a 15N label at Phe‐3 while the HIV‐1 peptide HFP‐UF8L9G10 was uniformly 13C and 15N labeled at Phe‐8, Leu‐9 and Gly‐10. The membrane composition of the IFP‐L2CF3N sample was POPC–POPG (4:1) and the membrane composition of the HFP‐UF8L9G10 sample was a mixture of lipids and cholesterol which approximately reflects the lipid headgroup and cholesterol composition of host cells of the HIV‐1 virus. In one‐dimensional magic angle spinning spectra, labeled backbone 13C were selectively observed using a REDOR filter of the 13C–15N dipolar coupling. Backbone chemical shifts were very similar at −50 and 20°C, which suggests that low temperature does not appreciably change the peptide structure. Relative to −50°C, the 20°C spectra had narrower signals with lower integrated intensity, which is consistent with greater motion at the higher temperature. The Leu‐2 chemical shift in the IFP‐L2CF3N sample correlates with a helical structure at this residue and is consistent with detection of helical structure by other biophysical techniques. Two‐dimensional 13C–13C correlation spectra were obtained for the HFP‐UF8L9G10 sample and were used to assign the chemical shifts of all of the 13C labels in the peptide. Secondary shift analysis was consistent with a β‐strand structure over these three residues. The high signal‐to‐noise ratio of the 2D spectra suggests that membrane‐associated fusion peptides with longer sequences of labeled amino acids can also be assigned with 2D and 3D methods. Copyright © 2004 John Wiley & Sons, Ltd.
15N T2′ relaxation times of bacteriorhodopsin transmembrane amide nitrogens
Authors: Soubias Olivier , Réat Valérie , Saurel Olivier , Milon Alain 
Published: January 2004

Abstract15N T2′ relaxation times of bacteriorhodopsin (BR) amide nitrogens were determined in the temperature range from 40 to −60°C using a Hahn echo pulse sequence and proton decoupling during the echo and detection times. Using oriented membrane samples, with their bilayer normal parallel to the external magnetic field, the 15N amide nitrogens belonging to the transmembrane helices could be selected for the analysis. The experiments were performed on purple membrane fragments (in which BR is organized in a 2D crystalline network) and on BR reconstituted into dimyristoylphosphatidylcholine at a 1:150 molar ratio (in which BR is in a freely diffusing monomeric state at 40°C and in an aggregated state at 4°C and below). The results are discussed in terms of helix dynamics, mosaic spread and resolution of the 15N spectra for the various samples and experimental conditions. Copyright © 2004 John Wiley & Sons, Ltd.
Conformational response of the phosphatidylcholine headgroup to bilayer surface charge: torsion angle constraints from dipolar and quadrupolar couplings in bicelles
Authors: Semchyschyn Darlene J. , Macdonald Peter M. 
Published: January 2004

AbstractThe effects of bilayer surface charge on the conformation of the phosphocholine group of phosphatidylcholine were investigated using a torsion angle analysis of quadrupolar and dipolar splittings in, respectively, 2H and 13C NMR spectra of 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine (POPC) labelled in the phosphocholine group with either deuterons (POPC‐α‐d2, POPC‐β‐d2 and POPC‐γ‐d9) or carbon‐13 (POPC‐α‐13C and POPC‐αβ‐13C2) and incorporated into magnetically aligned bicelles containing various amounts of either the cationic amphiphile 1,2‐dimyristoyl‐3‐trimethylammoniumpropane (DMTAP) or the anionic amphiphile 1,2‐dimyristoyl‐sn‐glycero‐3‐phosphoglycerol (DMPG). Three sets of quadrupolar splittings, one from each of the three deuteron labelling positions, and three sets of dipolar splittings (13Cα–31P, 13Cα–13Cβ, 13Cβ–14N), were measured at each surface charge, along with the 31P residual chemical shift anisotropy. The torsion angle analysis assumed fast anisotropic rotation of POPC about its long molecular axis, thus projecting all NMR interactions onto that director axis of motion. Dipolar, quadrupolar and chemical shift anisotropies were calculated as a function of the phosphocholine internal torsion angles by first transforming into a common reference frame affixed to the phosphocholine group prior to motional averaging about the director axis. A comparison of experiment and calculation provided the two order parameters specifying the director orientation relative to the molecule, plus the torsion angles α3, α4 and α5. Surface charge was found to have little effect on the torsion angle α5 (rotations about Cα–Cβ), but to have large and inverse effects on torsion angles α3 [rotations about P–O(11)] and α4 [rotations about O(11)–Cα], yielding a net upwards tilt of the P–N vector in the presence of cationic surface charge, and a downwards tilt in the presence of anionic surface charge, relative to neutrality. Copyright © 2004 John Wiley & Sons, Ltd.
Properties of polyunsaturated phosphatidylcholine membranes in the presence and absence of cholesterol
Authors: Epand Richard M. , Epand Raquel F. , Bain Alex D. , Sayer Brian G. , Hughes Donald W. 
Published: January 2004

AbstractMixtures of cholesterol with phosphatidylcholine species containing the polyunsaturated acyl chains arachidonoyl or docosahexaenoyl were studied by 13C magic angle spinning (MAS) NMR using both cross‐polarization and direct polarization, by 31P NMR and by differential scanning calorimetry. Several unique features of these systems were observed. The separation of cholesterol in crystalline form occurred at much lower molar fractions than with other forms of phosphatidylcholine. The crystals that were formed were sensitive to the history of the sample. At cholesterol molar fractions below 0.5, they dissolved into the membrane by sequential heating and cooling scans. With higher molar fractions of cholesterol, larger amounts of anhydrous crystals were formed after the first heating. This was accompanied by the formation of non‐lamellar phases. The cholesterol crystals that were formed generally were not observed by direct polarization 13C MAS NMR, even with delay times of 100 s. This suggests that the cholesterol crystals are in a more rigid state in mixtures with these lipids. This is in contrast with the terminal methyl group of the acyl chains that is too mobile to allow cross‐polarization using 1 ms contact times. Copyright © 2004 John Wiley & Sons, Ltd.
Lateral diffusion studied by pulsed field gradient NMR on oriented lipid membranes
Authors: Orädd Greger , Lindblom Göran 
Published: January 2004

AbstractThis mini‐review focuses on the utilization of pulsed magnetic field gradients to measure diffusional motion in systems of macroscopically oriented lipid bilayers. The NMR diffusion technique is proposed to have appreciable potential for future biophysical investigations in the field of membrane biology. Topics such as transport of molecules both across and in the plane of the membrane can be successfully studied, and the formation of lipid domains and their intrinsic dynamics can also be scrutinized. First, a short introduction to the NMR technique is given together with a brief discussion on methods of obtaining a good bilayer orientation. Then, a number of recent results on biophysical/biological membrane systems of great interest is presented, in which some unique conclusions on so‐called ‘raft membranes’ are reached. It is shown for systems with large two‐phase areas of liquid disordered and liquid ordered phases that lipid lateral diffusion is faster in the former phase and has a smaller apparent activation energy. Further, on the time‐scale of the experiments (50–250 ms), exchange between the two phases is fast in the phospholipid–cholesterol–water ternary system, whereas it is slow in the sphingomyelin–dioleoylphosphatidylcholine–cholesterol–water quaternary system. Copyright © 2004 John Wiley & Sons, Ltd.
‘Boomerang’‐like insertion of a fusogenic peptide in a lipid membrane revealed by solid‐state 19F NMR
Authors: Afonin Sergii , Dürr Ulrich H. N. , Glaser Ralf W. , Ulrich Anne S. 
Published: January 2004

AbstractSolid state 19F NMR revealed the conformation and alignment of the fusogenic peptide sequence B18 from the sea urchin fertilization protein bindin embedded in flat phospholipid bilayers. Single 19F labels were introduced into nine distinct positions along the wild‐type sequence by substituting each hydrophobic amino acid, one by one, with L‐4‐fluorophenylglycine. Their anisotropic chemical shifts were measured in uniaxially oriented membrane samples and used as orientational constraints to model the peptide structure in the membrane‐bound state. Previous 1H NMR studies of B18 in 30% TFE and in detergent micelles had shown that the peptide structure consists of two α‐helical segments that are connected by a flexible hinge. This helix–break–helix motif was confirmed here by the solid‐state 19F NMR data, while no other secondary structure (β‐sheet, 310‐helix) was compatible with the set of orientational constraints. For both α‐helical segments we found that the helical conformation extends all the way to the respective N‐ and C‐termini of the peptide. Analysis of the corresponding tilt and azimuthal rotation angles showed that the N‐terminal helix of B18 is immersed obliquely into the bilayer (at a tilt angle τ ≈ 54°), whereas the C‐terminus is peripherally aligned (τ ≈ 91°). The azimuthal orientation of the two segments is consistent with the amphiphilic distribution of side‐chains. The observed ‘boomerang’‐like mode of insertion into the membrane may thus explain how peptide binding leads to lipid dehydration and acyl chain perturbation as a prerequisite for bilayer fusion to occur. Copyright © 2004 John Wiley & Sons, Ltd.
Amyloidosis of Alzheimer's Aβ peptides: solid‐state nuclear magnetic resonance, electron paramagnetic resonance, transmission electron microscopy, scanning transmission electron microscopy and atomic force microscopy studies
Authors: Antzutkin Oleg N. 
Published: January 2004

AbstractAggregation cascade for Alzheimer's amyloid‐β peptides, its relevance to neurotoxicity in the course of Alzheimer's disease and experimental methods useful for these studies are discussed. Details of the solid‐phase peptide synthesis and sample preparation procedures for Alzheimer's β‐amyloid fibrils are given. Recent progress in obtaining structural constraints on Aβ‐fibrils from solid‐state NMR and scanning transmission electron microscopy (STEM) data is discussed. Polymorphism of amyloid fibrils and oligomers of the ‘Arctic’ mutant of Aβ(1–40) was studied by 1H,13C solid‐state NMR, transmission electron microscopy (TEM) and atomic force microscopy (AFM), and a real‐time aggregation of different polymorphs of the peptide was observed with the aid of in situ AFM. Recent results on binding of Cu(II) ions and Al–citrate and Al–ATP complexes to amyloid fibrils, as studied by electron paramagnetic resonance (EPR) and solid‐state 27Al NMR techniques, are also presented. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis and structure–activity relationship of new analogues of antistasin
Authors: Danalev Dantcho L. , Vezenkov Lyubomir T. , Grigorova Boryana 
Published: January 2004

AbstractIntensive investigation connected with the development of new anticoagulant agents for the treatment of cardiovascular diseases was carried out. Direct and specific inhibition of thrombin and Factor Xa–like serine proteases in the coagulation cascade has been the focus of many efforts to design novel anticoagulants over the past decade. This work reports the synthesis and biological activity of new anticoagulant peptide analogues of natural isoforms 2 and 3 of antistasin. In addition they include different tripeptide sequences in their molecules, which are highly active inhibitors of different serine proteases such as plasmin, trypsin, thrombin and Factor Xa. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
Novel carbohydrate‐induced modification of peptides: crystal structure and NMR analysis of ester‐bridged bicyclic galactose‐enkephalin adduct containing imidazolidinone moiety
Authors: Kojić‐Prodić Biserka , Perić Berislav , Roščić Maja , Novak Predrag , Horvat Štefica 
Published: January 2004

AbstractComparative studies based on x‐ray crystallography and NMR spectroscopy were used for structural characterization of the novel minor, imidazolidinone moiety containing, product 2b of the Maillard reaction obtained in vitro by using the galactose‐modified endogenous opioid pentapeptide leucine‐enkephalin (Tyr‐Gly‐Gly‐Phe‐Leu) 1. The x‐ray analysis uniquely defined the molecular structure as cyclo‐{N‐{[2‐[‐4)‐D‐galacto‐pentitol‐1‐yl]‐4‐(4‐hydroxybenzyl)‐5‐oxoimidazolidin‐1‐yl‐(1 → O]acetyl}glycyl‐L‐phenylalanyl‐L‐leucyl‐} (3), having an 18‐membered ring with an ester bond between the secondary (C4′) hydroxyl group of a D‐galacto‐pentitolyl residue and the C‐terminal carboxy group of leucine‐enkephalin. The absolute configuration of the new chiral centre at the imidazolidinone moiety was established as C2(S), indicating a cis arrangement of C2 and C4 substituents at the 5‐membered heterocyclic ring. The NMR analysis of compound 2b carried out in CH3CN‐d3 and DMSO‐d6, indicated the existence of two isomers in solution, differing only in the position of the ester group in the molecule. NMR data for the minor isomer (13%–16%) are in agreement with structure 3. The migratory tendency of the peptidyl group from the primary (2b) to the secondary hydroxyl group (3) of a D‐galacto‐pentitolyl residue in methanol/water solution was confirmed by RP HPLC analysis. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
Heteroclitic recognition of combinatorial TX1TX2T peptide mixtures by mucin‐2 protein specific monoclonal antibody
Authors: Windberg Emôke , Uray Katalin , Illyés Eszter , Skribanek Zsolt , Price Michael R. , Sebestyén Ferenc , Hudecz Ferenc 
Published: January 2004

AbstractThe mucin‐2 (MUC2) glycoprotein secreted by the epithelial cells of human colon may be abnormally under‐glycosylated in the case of cancer. Monoclonal antibody (mAb) 994 raised against the immunogenic part of the protein core, recognizes malignant human colon tissues as well as pentapeptides with TX1TX2T motif present in MUC2. Using a combinatorial approach and ELISA experiments it was found that mAb 994 is able to recognize peptides of the sub‐library TQTX2T very strongly, and to some extent also peptides from TETX2T, TLTX2T and TVTX2T sub‐libraries. Binding studies with peptides corresponding to the TQTX2T and TETX2T sub‐libraries showed that mAb 994 recognized only six peptides (IC50 = 9–208 µmol dm−3) from the 19 compounds of the TQTX2T sub‐library and only three peptides (IC50 = 3500–16700 µmol dm−3) from the ‘second‐best’ TETX2T sub‐library. The most pronounced mAb binding occurred when Gln was in position X1 and it was much weaker in the case of Glu, Val or Leu. As for X2 amino acids, the presence of Pro, Ala can provide a strong, while Tyr, Trp, Phe and Ser a weaker, peptide–antibody interaction. Data from this study suggest that pentapeptide TQTPT, whose sequence is present in the native protein, is bound most strongly. However, almost identical binding properties were observed with peptide TQTAT, whose sequence is not present in the protein. Apart from this, some other ‘heteroclitic’ peptides were found with a different rank in the binding‐hierarchy. Based on these peptides artificial compounds can be prepared as potential candidates for vaccine development. Results of this study also provide a rationale for understanding the molecular background of the heteroclitic nature of the MUC2 protein core specific mAb 994. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
An unsaturated peptidomimetic assembly derived from a carbohydrate
Authors: Chung Ying‐Kit , Claridge Timothy D. W. , Fleet George W. J. , Johnson Stephen W. , Jones John H. , Lumbard Keith W. , Stachulski Andrew V. 
Published: January 2004

AbstractA strategy has been established for the synthesis of peptidomimetics derived from unsaturated carbohydrates, and exemplified by the use of methyl 2,6‐anhydro‐7‐azido‐3,7‐deoxy‐4,5‐O‐isopropylidene‐D‐lyxo‐hept‐2‐enonate 9 as a dipeptide ‘monomer’ which can be elaborated from either end. Selective reduction of 9 gives a protected pseudodipeptide ester suitable for use as an amino component, and saponification gives an azido acid suitable for use as a carboxyl component. The ‘dimer’ product of coupling these two components with TBTU can be similarly elaborated at either end to give a ‘trimer’, and a further cycle of selective reduction and coupling gave a ‘tetramer’, 17, a pseudo‐octapeptide. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
New antitumour cyclic astin analogues: synthesis, conformation and bioactivity
Authors: Rossi Filomena , Zanotti Giancarlo , Saviano Michele , Iacovino Rosa , Palladino Pasquale , Saviano Gabriella , Amodeo Pietro , Tancredi Teodorico , Laccetti Paolo , Corbier Catherine , Benedetti Ettore 
Published: January 2004

AbstractAstins, antitumour cyclic pentapeptides, were isolated from the Aster tataricus. Their chemical structures, consist of a 16‐membered ring system containing a unique β,γ‐dichlorinated proline [Pro(Cl)2], other non‐coded amino acid residues and a cis conformation in one of the peptide bonds. The astin backbone conformation, along with the cis peptide bond in which the β,γ‐dichlorinated proline residue is involved, was considered to play an important role in their antineoplastic activities on sarcoma 180A and P388 lymphocytic leukaemia in mice, but the scope and potential applications of this activity remain unclear. With the aim at improving our knowledge of the conformational properties influencing the bioactivity in this class of compounds, new astin‐related cyclopeptides were synthesized differing from the natural products by the presence of some non‐proteinogenic amino acid residues: Aib, Abu, ‐(S)β3‐hPhe and a peptide bond surrogate (‐SO2‐NH‐). The analogues prepared c(‐Pro‐Thr‐Aib‐β3‐Phe‐Abu‐), c[Pro‐Thr‐Aib‐(S)β3‐hPhe‐Abu], c[Pro‐Abu‐Ser‐(S)β3‐hPheΨ(CH2‐SO2‐NH)‐Abu] and c[Pro‐Thr‐Aib‐(S)β3‐hPheΨ(CH2‐SO2‐NH)‐Abu] were synthesized by classical methods in solution and tested for their antitumour effect. These molecules were studied by crystal‐state x‐ray diffraction analysis and/or solution NMR and MD techniques. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
Indices of lifetime polydrug use among adolescents
Authors: Sneed Carl D , Morisky Donald E , Rotheram‐Borus Mary Jane , Lee Sung‐Jae , Ebin Vicki J 
Published: January 2004

AbstractThe functional equivalency for three indices of lifetime polydrug use was examined in a sample of adolescents (N=794). The following indices were included in analyses: (a) a count of lifetime self‐report of substances used; (b) an index weighted by the severity of the substances used; and (c) a hierarchical index of substance use. Analyses for each index was conducted twice with abstinent youth (no report of substances over their lifetime) included and excluded from analyses. Relationships between the indices with gender, age, ethnicity, and country of origin were examined. The only difference between the indices found was for ethnicity in the full sample. African Americans had higher scores on the hierarchical substance use index than Latinos or Asian/Pacific Islanders. With the exception of the relationship between the hierarchical index and ethnicity, the relationships between the other demographic variables with indices were consistent. Implications for utilizing the count or weighted index versus a hierarchical index of lifetime polydrug use are discussed.
The reciprocal relationship between early adolescent attachment and internalizing and externalizing problem behaviour
Authors: Buist Kirsten L. , Deković Maja , Meeus Wim , van Aken Marcel A.G. 
Published: January 2004

AbstractThe aim of the present study is to examine the reciprocal relationship between parental attachment and adolescent internalizing and externalizing problem behaviour. In this longitudinal study, 288 adolescents (mean age 13.5 years) reported on their attachment relationships with their parents and on problem behaviour three times, with 1‐year‐intervals between measurement waves. Results show that attachment and both indicators of adolescent problem behaviour remain stable over time, although there were differences in stability between constructs. Reciprocal negative effects were found between attachment and internalizing problem behaviour, and between attachment and externalizing problem behaviour.
Precipitation and Northern Hemisphere regimes
Authors: Raible Christoph C. , Luksch Ute , Fraedrich Klaus 
Published: January 2004

AbstractRainfall anomalies in a longterm integration of general circulation model highlight the non‐stationarity of the ocean–atmosphere coupling in the North Atlantic which becomes manifest in two regimes. Anti‐correlations between the precipitation in the tropical and subtropical western Atlantic illustrate the changes of the Hadley cell with El Niño/Southern Oscillation (ENSO).The precipitation anomaly pattern in the north eastern Atlantic resembles variations of the North Atlantic storm track and the North Atlantic Oscillation (NAO). In the hemispheric regime, where 40% of the NAO variability can be explained by ENSO, both precipitation pattern are connected, whereas in the regional regime the ENSO‐link with the North Atlantic storm track and the subtropical 500 hPa geopotential height disappears. Copyright © 2004 Royal Meteorological Society. Published by Elsevier Ltd. All rights reserved.
Evolution of multicellularity in Metazoa: comparative analysis of the subcellular localization of proteins in Saccharomyces, Drosophila and Caenorhabditis
Authors: Hazkani‐Covo Einat , Levanon Erez Y. , Rotman Galit , Graur Dan , Novik Amit 
Published: January 2004

AbstractA comparison of the subcellular assignments of proteins between the unicellular Saccharomyces cerevisiae and the multicellular Drosophila melanogaster and Caenorhabditis elegans was performed using a computational tool for the prediction of subcellular localization. Nine subcellular compartments were studied: (1) extracellular domain, (2) cell membrane, (3) cytoplasm, (4) endoplasmic reticulum, (5) Golgi apparatus, (6) lysosome, (7) peroxisome, (8) mitochondria, and (9) nucleus. The transition to multicellularity was found to be characterized by an increase in the total number of proteins encoded by the genome. Interestingly, this increase is distributed unevenly among the subcellular compartments. That is, a disproportionate increase in the number of proteins in the extracellular domain, the cell membrane, and the cytoplasm is observed in multicellular organisms, while no such increase is seen in other subcellular compartments.A possible explanation involves signal transduction. In terms of protein numbers, signal transduction pathways may be roughly described as a pyramid with an expansive base in the extracellular domain (the numerous extracellular signal proteins), progressively narrowing at the cell membrane and cytoplasmic levels, and ending in a narrow tip consisting of only a handful of transcription modulators in the nucleus. Our observations suggest that extracellular signaling interactions among metazoan cells account for the uneven increase in the numbers of proteins among subcellular compartments during the transition to multicellularity.