1,721,048 research outputs found
Conformational Studies of Human [15-2-aminohexanoic Acid]little Gastrin In Sodium Dodecyl-sulfate Micelles By H-1-nmr
No full textHuman little gastrin is a 17 amino acid peptide that adopts a random conformation in water and an ordered structure in sodium dodecyl sulfate (SDS) micelles as well as in trifluoroethanol (TFE). The circular dichroism spectra in these two media have the same shape, indicative of a similar preferred conformation [Mammi, S., Mammi, N. J., Foffani, M. T., Peggion, E., Moroder, L., & Wunsch, E. (1987) Biopolymers 26, S1-S10]. We describe here the assignment of the proton NMR resonances and the conformational analysis of [Ahx15]little gastrin in SDS micelles. Two-dimensional correlation techniques form the basis for the assignment. The conformational analysis utilizes NOE's, NH to CaH coupling constants, and the temperature coefficients of the amide chemical shifts. The NMR data indicate a helical structure in the N-terminal portion of the peptide. These results are compared with the conformation that we recently proposed for a minigastrin analogue (fragment 5-17 of [Ahx15]little gastrin) in TFE
Determination of the secondary structural elements of chicken liver Fatty Acid Binding Protein by two-homonuclear NMR
No full textA conformational study in solution of the fatty acid binding protein from chicken liver is presented. The nearly complete sequence-specific 1H resonance assignment was achieved from homonuclear two-dimensional nmr experiments using a sample of native protein. The principal elements of secondary structure were identified: 10 antiparallel beta-strands and one helical segment followed by a turn comprising 5 residues. These elements correspond closely with those of the crystal structure of the related protein, and two new secondary structural features obtained from the nmr data are the beta-sheet conformation between the first and the last beta-strand in the protein sequence, as well as a helical loop at the N-terminus of the polypeptide chain
Macromolecularization of a tripeptide analog of the Cu(II) binding site of human serum albumin. I. Synthesis, conformation, and binding properties of a Gly-Gly-His derivative of poly(L-lysine)
No full textThe side chain of poly(L-Lysine) was derivatized with the tripeptide Gly-Gly-His, a good imetic of the Cu(II) binding site of serum albumin. The aim was to obtain a macromolecular adduct with high affinity for Cu(II) ions. We describe the synthesis and the preliminary conformational properties of this adduct, which exhibits strong affinity toward Cu(II) and Ni(II)
1H Nuclear Magnetic Resonance Spectra of Chloroform Extracts of Honey for Chemometric Determination of Its Botanical Origin
No full textIn this work, we present a new NMR study, coupled with chemometric analysis, on nonvolatile organic honey components. The extraction method is simple and reproducible. The 1H NMR spectra of chloroform extracts acquired with a fast and new pulse sequence were used to characterize and differentiate by chemometric analysis 118 honey samples of four different botanical origins (chestnut, acacia, linden, and polyfloral). The spectra collection, processing, and analysis require only 30 min. The 1H spectrum provides a fingerprint for each honey type, showing many characteristic peaks in all spectral regions. Principal component analysis (PCA) and projection to latent structures by partial least squares-discriminant analysis (PLS-DA) were performed on selected signals of the spectra to discriminate the different botanical types and to identify characteristic metabolites for each honey type. A distinct discrimination among samples was achieved. According to the distance to model criterion, there was no overlap between the four models, which proved to be specific for each honey type. The PLS-DA model obtained has a correlation coefficient R2 of 0.67 and a validation correlation coefficient Q2 of 0.77. The discriminant analysis allowed us to classify correctly 100% of the samples. A classification index can be calculated and used to determine the floral origin of honey as an alternative to the melissopalinology test and possibly to determine the percentage of various botanical species in polyfloral samples. Preliminary data on the identification of marker compounds for each botanical origin are presented
Conformation and interactions of bioactive peptides from insect venoms: The bombolitins
No full textBombolitins are five structurally related heptadecapeptides originally isolated from the venom of a bumblebee, acting at membrane level and able to enhance the activity of Phospholipase A(2). The biological activity of this class of natural peptides seems to be related to the their ability to form amphiphilic helical structures in the presence of phospholipid aggregates or related membrane model systems. We have carried out systematic investigations on a series of bombolitins and their synthetic analogs in order to establish the conditions in which amphipathic helices are formed and to elucidate the details of the interaction with phospholipids and related model systems. We have shown that bombolitins and their analogs interact with phospholipid aggregates and detergent micelles forming amphiphilic helices. By means of the Langmuir film balance technique, coupled with fluorescence microscopy, we have shown that bombolitins perturbe the structure of phospholipid monolayers, forming phase separated peptide domains. In aqueous solution, in the absence of detergent or phospholipids, bombolitins form oligomeric aggregates with consequent conformational transition from a random coil to an ct-helical structure. In the aggregate structure, evidence was obtained that helices are oriented in an antiparallel fashion. In this article we summarize the most recent results of conformational studies by CD, NMR and computer simulations on a series of bombolitins and retro-, all-D- and all-D-retro-analogs. (C) 1998 John Wiley & Sons, Inc
Conformational Studies of Human Des-trp1,nle12-minigastrin In Water Trifluoroethanol Mixtures By H-1-nmr and Circular-dichroism
No full textThe 1H NMR spectrum of the title peptide, H-Leu-(Glu)5-Ala-Tyr-Gly-Trp-Nle-Asp-Phe-NH, in 90% H2O/10% D2O was assigned by two-dimensional methods, and the displacement of the proton resonances upon addition of 2,2,2-trifluoroethanol (TFE) was followed. This permitted the assignment of the spectrum in 90% TFE/10% D2O. While the water conformation of the minigastrin analogue is random, the CD spectrum indicates that an ordered structure is present in TFE. Variable-temperature NMR data in this medium show that six amide protons have low temperature coefficients, two of the five Glu's, Trp, Nle, Asp, and Phe. These results were interpreted in terms of an a-helical stretch comprising the Leu and the five Glu residues and a 310-helix initiated by a b-turn at the sequence -Ala-Tyr-Gly-Trp-. Both CD and NMR data at different solvent compositions show two regions of conformational change, between 20 and 25% water and above 60% water
Conformations of Bombolitin-I and Bombolitin-III In Aqueous-solutions - Circular-dichroism, H-1-nmr, and Computer-simulation Studies
No full textThe heptadecapeptides bombolitin I and bombolitin III are two of a series of peptides postulated to be biologically active within a membrane environment. In the preceding paper [Bairaktari, E., Mierke, D. F., Mammi, S., & Peggion, E. (1990) Biochemistry (preceding paper in this issue)] the conformational preferences of these peptides in the presence of SDS surfactant micelles, a mimetic for biological membranes, were examined. During these studies the conformations of these peptides were investigated in aqueous solutions by circular dichroism and nuclear magnetic resonance. A large difference was observed for the two peptides. Bombolitin I lacks any observable secondary structure in aqueous solution, independent of temperature, pH, and concentration. In striking contrast, bombolitin III adopts a well-defined a-helix at concentrations greater than 1.3 mM. This is indeed surprising given the great similarity of the two peptides. The a-helix of bombolitin III is pH dependent, with a great decrease in the observed secondary structure at pH values below 3.5. This observation could only be due to the protonation of the Asp residue at the fifth position. These findings suggest that the secondary structure arises from molecular aggregation of bombolitin III through the formation of a salt bridge involving the Asp side chain. The a-helix observed at “high” concentration (>2.5 mM) has been characterized by CD and by the NOE’s measured throughout a majority of the peptide. The experimentally determined structure has been energy refined with restrained molecular dynamics. The conformational results from this study are then compared with the conformations found in the presence of surfactant micelles
Conformational Studies By Circular-dichroism, H-1-nmr, and Computer-simulations of Bombolitin-I and Bombolitin-III In Aqueous-solution Containing Surfactant Micelles
No full textThe heptadecapeptides bombolitin I and bombolitin III are two of a series of peptides postulated
to be biologically active within a membrane environment. In the preceding paper [Bairaktari, E., Mierke, D. F., Mammi, S., & Peggion, E. (1990) Biochemistry (preceding paper in this issue)] the conformational preferences of these peptides in the presence of SDS surfactant micelles, a mimetic for biological membranes, were examined. During these studies the conformations of these peptides were investigated in aqueous solutions by circular dichroism and nuclear magnetic resonance. A large difference was observed for the two peptides. Bombolitin I lacks any observable secondary structure in aqueous solution, independent of temperature, pH, and concentration. In striking contrast, bombolitin III adopts a well-defined a-helix at concentrations greater than 1.3 mM. This is indeed surprising given the great similarity of the two peptides.
The a-helix of bombolitin III is pH dependent, with a great decrease in the observed secondary structure
at pH values below 3.5. This observation could only be due to the protonation of the Asp residue at the
fifth position. These findings suggest that the secondary structure arises from molecular aggregation of bombolitin III through the formation of a salt bridge involving the Asp side chain. The a-helix observed at “high” concentration (>2.5 mM) has been characterized by CD and by the NOE’s measured throughout a majority of the peptide. The experimentally determined structure has been energy refined with restrained molecular dynamics. The conformational results from this study are then compared with the conformations found in the presence of surfactant micelles
Synthesis and structural studies of new analogues of PTH(1-11) containing C-alpha-tetra-substituted amino acids in position 8
No full textThe N-terminal 1–34 fragment of parathyroid hormone (PTH) is fully active in vitro and in vivo and it can reproduce all biological responses characteristic of the native intact PTH. Recently, analogues of PTH(1–11) fragments with helicity-enhancing substitutions have been demonstrated to yield potent analogues of PTH(1–34). The work describes the synthesis, biological activity and structure of analogues of the best modified PTH sequence H-Aib-Val-Aib-Glu-Ile-Gln-Leu-Nle-His-Gln-Har-NH2 (I). In particular, the effect of the Ala/Aib substitution at positions 1 and 3 as well as of the replacement of Nle in position 8 with D-Nle, L-(αMe)-Nle and D-(αMe)-Nle was studied. The resulting peptides were characterized structurally by CD spectroscopy, solution NMR and MD, and in vitro for activity with respect to the cognate receptor, parathyroid hormone receptor
The 11-mer repeats of human α−synuclein in vesicle interactions and lipid composition discrimination: a cooperative role.
No full textalpha-Synuclein is a protein abundant in presynaptic terminals in the brain. The N-terminal region of the sequence contains an imperfect 11-residue periodicity also found in A-class apolipo-proteins and able to fold into an amphipathic helix. Here, the ability of three fragments of the protein, which include one, two, and all repeats, respectively, to bind to vesicles of different phospholipid composition is described. The results suggest a cooperative action of the repeals in selecting tat-get membranes for interaction based on their lipid composition. This deduction is possibly related to the physiological role of the protein, which is still poorly understood
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