Biomedical subjects

Barbara Lelli

Publications and source records attributed to Barbara Lelli.

10 recordsLinked to original sources

PubMed2006

NMR studies of BPTI aggregation by using paramagnetic relaxation reagents.

Paramagnetic probes, whose approach to proteins can be monitored by nuclear magnetic resonance (NMR) studies, have been found of primary relevance for investigating protein surfaces accessibility. Here, paramagnetic probes are also suggested for a systematic investigation on protein aggregation. Bovine pancreatic trypsin inhibitor (BPTI) was used as a model system for aggregation by analyzing its interaction with TEMPOL and Gd(III)DTPA-BMA. Some of the measured paramagnetic relaxation rates of BPTI protons exhibited a reverse dependence on protein concentration, which can be attributed to the formation of transient BPTI aggregates.

Animals↗

PubMed2006

Stable peptide inhibitors prevent binding of lethal and oedema factors to protective antigen and neutralize anthrax toxin in vivo.

The lethal and oedema toxins produced by Bacillus anthracis, the aetiological agent of anthrax, are made by association of protective antigen with lethal and oedema factors and play a major role in the pathogenesis of anthrax. In the present paper, we describe the production of peptide-based specific inhibitors in branched form which inhibit the interaction of protective antigen with lethal and oedema factors and neutralize anthrax toxins in vitro and in vivo. Anti-protective antigen peptides were selected from a phage library by competitive panning with lethal factor. Selected 12-mer peptides were synthesized in tetra-branched form and were systematically modified to obtain peptides with higher affinity and inhibitory efficiency.

Amino Acid Sequence↗

PubMed2005

Antimicrobial activity of novel dendrimeric peptides obtained by phage display selection and rational modification.

A large 10-mer phage peptide library was panned against whole Escherichia coli cells, and an antimicrobial peptide (QEKIRVRLSA) was selected. The peptide was synthesized in monomeric and dendrimeric tetrabranched form (multiple antigen peptide [MAP]), which generally allows a dramatic increase of peptide stability to peptidases and proteases. The antibacterial activity of the dendrimeric peptide against E. coli was much higher than that of the monomeric form. Modification of the original sequence, by residue substitution or sequence shortening, produced three different MAPs, M4 (QAKIRVRLSA), M5 (KIRVRLSA), and M6 (QKKIRVRLSA) with enhanced stability to natural degradation and antimicrobial activity against a large panel of gram-negative bacteria. The MICs of the most potent peptide, M6, were as low as 4 to 8 microg/ml against recent clinical isolates of multidrug-resistant Pseudomonas aeruginosa and members of the Enterobacteriaceae. The same dendrimeric peptides showed high stability to blood proteases, low hemolytic activity, and low cytotoxic effects on eukaryotic cells, making them promising candidates for the development of new antibacterial drugs.

Anti-Bacterial Agents↗

PubMed2004

NMR and MD studies on the interaction between ligand peptides and alpha-bungarotoxin.

The interaction between alpha-bungarotoxin and linear synthetic peptides, mimotope of the nicotinic acetylcholine receptor binding site, has been characterised extensively by several methods and a wealth of functional, kinetic and structural data are available. Hence, this system represents a suitable model to explore in detail the dynamics of a peptide-protein interaction. Here, the solution structure of a new complex of the protein toxin with a tridecapeptide ligand exhibiting high affinity has been determined by NMR. As observed for three other previously reported mimotope-alpha-bungarotoxin complexes, also in this case correlations between biological activity and kinetic data are not fully consistent with a static discussion of structural data. Molecular dynamics simulations of the four mimotope-toxin complexes indicate that a relevant contribution to the complex stability is given by the extent of the residual flexibility that the protein maintains upon peptide binding. This feature, limiting the entropy loss caused by protein folding and binding, ought to be generally considered in a rational design of specific protein ligands.

Bungarotoxins↗

PubMed2003

Synthetic peptides in the form of dendrimers become resistant to protease activity.

In previous papers, we observed that dendrimers of peptide mimotopes of the nicotinic receptor ligand site are strong antidotes against the lethality of the nicotinic receptor ligand alpha-bungarotoxin. Although their in vitro activity is identical to that of dendrimers, the corresponding monomeric peptide mimotopes are not effective in vivo. Because the higher in vivo efficiency of dendrimers could not in this case be related to polyvalent interaction, the stability to blood protease activity of monomeric versus tetrabranched dendrimeric mimotope peptides was compared here by incubating three different mimotopes with human plasma and serum. Unmodified peptides and cleaved sequences were followed by high pressure liquid chromatography and mass spectrometry. Tetrabranched peptides were shown to be much more stable in plasma and also in serum. To assess the notable stability of multimeric peptides, different bioactive neuropeptides, including enkephalins, neurotensin and nociceptin, were synthesized in monomeric and tetrabranched forms and incubated with human plasma and serum and with rat brain membrane extracts. All the tetrabranched neuropeptides fully retained biological activity and generally showed much greater stability to blood and brain protease activity. Some tetrabranched peptides were also resistant to trypsin and chymotrypsin. Our findings provide new insights into the possible therapeutic use of bioactive peptides.

Animals↗

PubMed2003

Biochemical filtering of a protein-protein docking simulation identifies the structure of a complex between a recombinant antibody fragment and alpha-bungarotoxin.

The structural characterization of a complex of alpha-bungarotoxin with a recombinant antibody fragment that mimics the acetylcholine receptor was achieved using docking simulation procedures. To drive the computer simulation towards a limited set of solutions with biological significance, a filter, incorporating general considerations of antigen-antibody interactions, specificity of the selected antibody fragment and results from alpha-bungarotoxin epitope mapping, was adopted. Two similar structures were obtained for the complex, both of them stabilized by cation-pi and hydrophobic interactions due to tyrosilyl residues of the antibody fragment. Site-directed mutagenesis studies, removing each of the latter aromatic residues and causing full inactivation of the interaction process between the antibody fragment and the neurotoxin, support the validity of the calculated structure of the complex.

Amino Acid Sequence↗

PubMed2003

Rational design and molecular diversity for the construction of anti-alpha-bungarotoxin antidotes with high affinity and in vivo efficiency.

The structure of peptide p6.7, a mimotope of the nicotinic receptor ligand site that binds alpha-bungarotoxin and neutralizes its toxicity, was compared to that of the acetylcholine binding protein. The central loop of p6.7, when complexed with alpha-bungarotoxin, fits the structure of the acetylcholine binding protein (AChBP) ligand site, whereas peptide terminal residues seem to be less involved in toxin binding. The minimal binding sequence of p6.7 was confirmed experimentally by synthesis of progressively deleted peptides. Affinity maturation was then achieved by random addition of residues flanking the minimal binding sequence and by selection of new alpha-bungarotoxin binding peptides on the basis of their dissociation kinetic rate. The tetra-branched forms of the resulting high-affinity peptides were effective as antidotes in vivo at a significantly lower dose than the tetra-branched lead peptide.

Amino Acid Sequence↗

PubMed2002

A branched peptide mimotope of the nicotinic receptor binding site is a potent synthetic antidote against the snake neurotoxin alpha-bungarotoxin.

We previously produced synthetic peptides mimicking the snake neurotoxin binding site of the nicotinic receptor. These peptide mimotopes bind the snake neurotoxin alpha-bungarotoxin with higher affinity than peptides reproducing native receptor sequences and inhibit toxin binding to nicotinic receptors in vitro; yet their efficiency in vivo is low. Here we synthesized one of the peptide mimotopes in a tetrabranched MAP form. The MAP peptide binds alpha-bungarotoxin in solution and inhibits its binding to the receptor with a K(A) and an IC(50) similar to the monomeric peptide. Nonetheless, it is at least 100 times more active in vivo. The MAP completely neutralizes toxin lethality when injected in mice at a dose compatible with its use as a synthetic antidote in humans. The in vivo efficacy of the tetrameric peptide cannot be ascribed to a kinetic and thermodynamic effect and is probably related to different pharmacokinetic behavior of the tetrameric molecule, with respect to the monomer. Our findings bring new perspectives to the therapeutic use of multimeric peptides.

Animals↗

PubMed2002

NMR structure of alpha-bungarotoxin free and bound to a mimotope of the nicotinic acetylcholine receptor.

A combinatorial library approach was used to produce synthetic peptides mimicking the snake neurotoxin binding site of nicotinic receptors. Among the sequences, which inhibited binding of alpha-bungarotoxin to muscle and neuronal nicotinic receptors, HRYYESSLPWYPD, a 14-amino acid peptide with considerably higher toxin-binding affinity than the other synthesized peptides, was selected, and the structure of its complex with the toxin was analyzed by NMR. Comparison of the solution structure of the free toxin and its complex with this peptide indicated that complex formation induced extensive conformational rearrangements mainly at finger II and the carboxy terminus of the protein. The peptidyl residues P10 and Y4 seemed to be critical for peptide folding and complex stability, respectively. The latter residue of the peptide strongly interacted with the protein by entering a small pocket delimited by D30, C33, S34, R36, and V39 toxin side chains.

Animals↗

PubMed2002

Peptide-protein interactions studied by surface plasmon and nuclear magnetic resonances.

The structural features of the complexes that alpha-bungarotoxin forms with three different synthetic peptides, mimotopes of the nicotinic acetylcholine receptor binding site, have been compared to the corresponding nuclear magnetic resonance (NMR) and surface plasmon resonance (SPR) data. For the considered peptides, the observed different affinities towards the toxin could not be accounted simply by static structural considerations. A combined analysis of the SPR- and NMR-derived dynamic parameters shows new correlations between complex formation and dissociation and the overall pattern of intramolecular and intermolecular nuclear Overhauser effects. These features could be crucial for a rational design of protein ligands.

Amino Acid Sequence↗