Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Melitten”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
PubMed2003

D-amino acid residues in peptides and proteins.

We have investigated the D-amino acid residues present in Protein Data Bank (PDB) entries, categorizing them into "real" D-residues and artifacts. In polypeptide chains of more than 20 residues, only a single instance of a "real" D-residue, other than those deliberately designed or engineered, was found. This example was the result of a slow chemical epimerization process. Another 12 designed D-residues were found in these longer polypeptide chains. Smaller peptides of 20 or fewer residues contained 479 "real" D-residues, the majority in various gramicidin, actinomycin, or cyclosporin structures. We found 148 PDB entries with "real" D-residues and a further 186, in which all apparent D-residues are artifacts. Investigating the (phi, psi) preferences of the "real" D-residues, we found that the region around (-60 degrees, -45 degrees ) was almost completely unoccupied, even though it is not formally disallowed. We link the low propensity to occupy this region with the alpha-helix destabilizing properties of D-residues.

Amino Acids↗
PubMed2003

Effective energy function for proteins in lipid membranes.

A simple extension of the EEF1 energy function to heterogeneous membrane-aqueous media is proposed. The extension consists of (a) development of solvation parameters for a nonpolar phase using experimental data for the transfer of amino acid side-chains from water to cyclohexane, (b) introduction of a heterogeneous membrane-aqueous system by making the reference solvation free energy of each atom dependent on the vertical coordinate, (c) a modification of the distance-dependent dielectric model to account for reduced screening of electrostatic interactions in the membrane, and (d) an adjustment of the EEF1 aqueous model in light of recent calculations of the potential of mean force between amino acid side-chains in water. The electrostatic model is adjusted to match experimental observations for polyalanine, polyleucine, and the glycophorin A dimer. The resulting energy function (IMM1) reproduces the preference of Trp and Tyr for the membrane interface, gives reasonable energies of insertion into or adsorption onto a membrane, and allows stable 1-ns MD simulations of the glycophorin A dimer. We find that the lowest-energy orientation of melittin in bilayers varies, depending on the thickness of the hydrocarbon layer.

Amino Acids↗
PubMed2004

Melittin as model system for probing interactions between proteins and cyclodextrins.

Cylcodextrin sugars are cyclic sugars that have a hydrophilic exterior and a hydrophobic center. This enables cyclodextrins to solubilize hydrophobic molecules in aqueous media. Cyclodextrins may inhibit aggregation by intercalating surface aromatic residues and competing with interprotein aromatic clusters (pi-pi interactions). In order to investigate this concept, the interaction of hydroxypropyl-beta-cyclodextrin (HPBCD) with melittin is studied with steady-state and time-resolved fluorescence, fluorescence polarization, circular dichroism, and IR spectroscopy. HPBCD inhibits the aggregation of melittin. This inhibition and the spectroscopic results are consistent with the lone aromatic tryptophan of the peptide being intercalated within HPBCD.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed2005

Implicit solvent simulations of peptide interactions with anionic lipid membranes.

A recently developed implicit membrane model (IMM1) is supplemented with a Gouy-Chapman term describing counterion-screened electrostatic interactions of a solute with negatively charged membrane lipids. The new model is tested on peptides that bind to anionic membranes. Pentalysine binds just outside the plane of negative charge, whereas Lys-Phe peptides insert their aromatic rings into the hydrophobic core. Melittin and magainin 2 bind more strongly to anionic than to neutral membranes and in both cases insert their hydrophobic residues into the hydrocarbon core. The third domain of Antennapedia homeodomain (penetratin) binds as an alpha-helix in the headgroup region. Cardiotoxin II binds strongly to anionic membranes but marginally to neutral ones. In all cases, the location and configuration of the peptides are consistent with experimental data, and the effective energy changes upon binding compare favorably with experimental binding free energies. The model opens the way to exploring the effect of membrane charge on the location, conformation, and dynamics of a large variety of biologically active peptides on membranes.

Animals↗
PubMed2005

Understanding the energetics of helical peptide orientation in membranes.

Understanding the energetic factors determining the positioning and orientation of single-helical peptides in membranes is of fundamental interest in structural biology. Here, a simple 5-slab continuum dielectric model for the membrane is examined that distinguishes between the solvent, headgroup, and core regions. An analytical solution for the electrostatic solvation of a single dipole and an all-atom model of N-methylacetamide are used to demonstrate the effect of the dielectric boundaries in the system on peptide dipole orientation. The dipole orientation energy is shown to dominate the electrostatic solvation energy of a polyalanine helix in the membrane. With an additional surface-area-dependent term to account for the cavity formation in the aqueous region, the continuum electrostatics description is used to examine several helical peptides, the atoms of which are explicitly represented with a molecular mechanics force field. The experimentally determined tilt angles of a number of peptides of alternating alanine and leucine residues, and of glycophorin and melittin, are accurately reproduced by the model. The factors determining the tilt angles and their fluctuations are analyzed. The tilt angles of the simpler peptides are found to increase approximately linearly with peptide length; this effect is also rationalized. The analysis and model presented here provide a step toward the prediction of helical membrane protein structure.

Acetamides↗
PubMed1986

Protein fluorescence quenching by small molecules: protein penetration versus solvent exposure.

Experiments were done to test the thesis that acrylamide and similar small molecules can penetrate into proteins on a nanosecond time scale. The approach taken was to measure the pattern of fluorescence quenching exhibited by quenching molecules differing in molecular character (size, polarity, charge) when these are directed against protein tryptophans that cover the whole range of tryptophan accessibility. If quenching involves protein penetration and internal quencher migration, one expects that larger quenchers and more polar quenchers should display lesser quenching. In fact, no significant dependence on quencher character was found. For proteins that display measurable quenching, the disparate quenchers studied display very similar quenching rate constants when directed against any particular protein tryptophan. For several proteins having tryptophans known to be buried, no quenching occurs. These results are not consistent with the view that the kinds of small molecules studied can quite generally penetrate into and diffuse about within proteins at near-diffusion-limited rates. Rather the results suggest that when quenching is observed, the pathway involves encounters with tryptophans that are partially exposed at the protein surface. Available crystallographic results support this conclusion.

Alcohol Dehydrogenase↗
PubMed1988

The aggregation state of spin-labeled melittin in solution and bound to phospholipid membranes: evidence that membrane-bound melittin is monomeric.

Spin-labeled derivatives of the bee venom protein, melittin, were obtained by reacting on the average one of the four amino groups of the protein with succinimidyl-2,2,5,5-tetramethyl-3-pyrroline-1-oxyl-3-carboxylate. All 16 statistically possible reaction products with 0, 1, 2, 3 or 4 spin labels per protein were then separated in a single pass with reversed phase high performance liquid chromatography. With the help of trypsin digestion and diode array detection it was possible to assign the primary structure of all 16 eluting fractions. All fractions with only one spin label per protein were purified for electron paramagnetic resonance measurements. The labeling sites cover different regions of the protein: one is at the N-terminus, one at lysine-7, and two are near the C-terminus at lysine-21 and lysine-23, respectively. This set of specifically labeled melittins was used to study the structure and dynamics of melittin in aqueous solutions and when bound to neutral or negatively charged membranes. In aqueous solution a reduction in rotational correlation time and appearance of spin-spin interaction was observed during salt-induced transition from a random coil monomer to a mostly alpha-helical tetramer. Membrane binding to phospholipid bilayers in low or high ionic strength was reflected only in a further decrease in mobility. The absence of any spin interaction in the membrane-bound state suggests that melittin is monomeric under these conditions. All derivatives were able to detect these structural changes, but melittin labeled at the N-terminal amino group was especially valuable. Because of postulated intramolecular hydrogen bonding, this label reflects directly the motion of the entire protein or tetramer. Broadening experiments with chromium oxalate show that all labeled sites are at least partially exposed to the aqueous phase when melittin is bound to membranes. This suggests that an alpha-helical melittin monomer binds to membranes with its axis parallel to the membrane surface.

Bee Venoms↗
PubMed1990

Model for the interaction of amphiphilic helices with troponin C and calmodulin.

Crystals of troponin C are stabilized by an intermolecular interaction that involves the packing of helix A from the N-terminal domain of one molecule onto the exposed hydrophobic cleft of the C-terminal domain of a symmetry related molecule. Analysis of this molecular recognition interaction in troponin C suggests a possible mode for the binding of amphiphilic helical molecules to troponin C and to calmodulin. From the template provided by this troponin C packing, it has been possible to build a model of the contact region of mastoporan as it might be bound to the two Ca2+ binding proteins. A possible binding mode of melittin to calmodulin is also proposed. Although some of the characteristics of binding are similar for the two amphiphilic peptides, the increased length of melittin requires a significant bend in the calmodulin central helix similar to that suggested recently for the myosin light chain kinase calmodulin binding peptide (Persechini and Kretsinger: Journal of Cardiovascular Pharmacology 12:501-512, 1988). Not only are the hydrophobic interactions important in this model, but there are several favorable electrostatic interactions that are predicted as a result of the molecular modeling. The regions of troponin-C and calmodulin to which amphiphilic helices bind are similar to the regions to which the neuroleptic drugs such as trifluoperazine have been predicted to bind (Strynadka and James: Proteins 3:1-17, 1988).

Amino Acid Sequence↗
PubMed1990

Models of delta-hemolysin membrane channels and crystal structures.

Molecular modeling and energy calculations have been used to study how delta-hemolysin and melittin helices may aggregate on membrane surfaces and insert through membranes to form channels. In these models adjacent antiparallel amphipathic helices form planar "raft" structures, in which one surface is hydrophobic and the other hydrophilic. Models of delta-hemolysin crystal structure were developed using these "rafts." These models are based on the unit cell constants and the crystal symmetry obtained from the preliminary crystal data. Energy calculations favor channel models of delta-hemolysin with six or eight monomers per channel.

Amino Acids↗
PubMed1991

Refined structure of melittin bound to perdeuterated dodecylphosphocholine micelles as studied by 2D-NMR and distance geometry calculation.

In our previous paper we reported the conformation of melittin bound to perdeuterated dodecylphosphocholine micelles as studied by 1H NMR experiment and distance geometry calculation. No hydrogen bonds were taken into consideration explicitly in the calculation. However, mostly alpha-helical conformations were obtained as results of the calculation even with no explicitly assumed hydrogen bonds. In the present paper we refined the distance geometry calculation by incorporating hydrogen bonds suggested by the previous calculation. As a result, we obtained the conformation of melittin, which was consistent with both NMR data and the additional hydrogen bonding data. The alpha-helical rod in the refined conformation also has a kink at Thr-11 and Gly-12, but its bent angle is now a bit narrowly distributed in 135 degrees +/- 15 degrees. In the present study another distortion at Trp-19 and IIe-20 becomes conspicuous. The average root-mean-square displacement of atoms is now much smaller and is 1.5 A for all backbone atoms. In the present paper side chain conformations are also analyzed.

Deuterium↗
PubMed1993

Insertion of peptide chains into lipid membranes: an off-lattice Monte Carlo dynamics model.

A combination of dynamic Monte Carlo simulation techniques with a hydropathy scale method for the prediction of the location of transmembrane fragments in membrane proteins is described. The new hydropathy scale proposed here is based on experimental data for the interactions of tripeptides with phospholipid membranes (Jacobs, R.E., White, S.H. Biochemistry 26:6127-6134, 1987) and the self-solvation effect in protein systems (Roseman, M.A. J. Mol. Biol. 200:513-522, 1988). The simulations give good predictions both for the state of association and the orientation of the peptide relative to the membrane surface of a number of peptides including Magain2, M2 delta, and melittin. Furthermore, for Pf1 bacteriophage coat protein, in accord with experiment, the simulations predict that the C-terminus forms a transmembrane helix and the N-terminus forms a helix which is adsorbed on the surface of the bilayer. Finally, the present series of simulations provide a number of insights into the mechanism of insertion of peptides into cell membranes.

Algorithms↗
PubMedDate not supplied

Immunogenicity of dinitrocarboxyphenylated melittin: the influence of C-terminal chain shortening, N-terminal substitution and prolin insertion at positions 5 and 10.

Peptides derived from the bee-venom melittin were fitted with the haptenic group dinitrocarboxyphenyl (Dncp) and tested in out-bred guinea pigs for immunogenicity by measuring the IgG anti-Dncp antibody response by ELISA. Dncp-conjugates comprising virtually the entire melittin proved to be strong immunogens producing antibody responses comparable to those of proteins. Weak responses were obtained with considerably shortened sequences. Conjugates with N-terminal Dncp gave markedly reduced antibody responses compared to peptides with C-terminal Dncp. An N-terminal biotinyl substituent abolished the immune response whereas N-terminal lauryl and caprylyl had little effect. Insertion of L-proline into a hexadecapeptide conjugate abolishing the possibility of helix formation gave an immunogen to which individual animals clearly responded on a low level. Oligomerisation, but not the cytolytic activity of melittin peptides, may contribute to the immunogenicities observed.

Animals↗
PubMed2002

HP (2-20) derived from the amino terminal region of helicobacterpylori ribosomal protein L1 exerts its antifungal effects by damaging the plasma membranes of Candida albicans.

The fungicidal effects of the peptide HP (2-20). derived from the N-terminal sequence of Helicobacter pylori ribosomal protein L1 (RPL1). have been investigated. HP (2-20) displays a strong fungicidal activity against various fungi, without haemolytic activity against human erythrocyte cells, and the fungicidal activity is inhibited by Ca2+ and Mg2+ ions. In order to investigate the fungicidal mechanism(s) of HP (2-20). the amount of intracellular trehalose was measured in C. albicans. It was found that the amounts of intracellular trehalose were decreased when HP (2-20) was used. The action of the peptide against fungal cell membranes was further examined by the potassium-release test; HP (2-20) was found to increase the amount of K+ released from the cells. Furthermore, HP (2-20) caused significant morphological changes, as shown by scanning electron microscopy, and by testing the membrane disrupting activity using liposomes (phosphatidyl choline/cholesterol; 10: 1, w/w). Our results suggest that HP (2-20) may exert its antifungal activity by disrupting the structure of cell membranes, via pore formation or direct interaction with the lipid bilayers.

Amino Acid Sequence↗
PubMedDate not supplied

Hydrophobic effects on antibacterial and channel-forming properties of cecropin A-melittin hybrids.

The design of cecropin-melittin hybrid analogues is of interest due to the similarities in the structure of the antimicrobial peptides cecropin and melittin but differences in their lytic properties. We suspected that a hydrophobic residue in position 2 of milittin (Ile8 in the hybrid) plays an important role in the activity of the 15-residue hybrid, KWKLFKKIGAVLKVL-NH2, [CA(1-7)M(2-9)NH2] and have now examined its role in the analogue toward five test bacteria. Deletion of Ile8 reduced activity, and it was not restored by lengthening to 15 residues by addition of another threonine at the C-terminus. Replacement of Ile8 by a hydrophobic leucine maintained good activity and Ala8 was equally active for four organisms, although less active against Staphylococcus aureus. Replacement by the hydrophilic Ser8 strongly reduced potency against all five organisms. Deletion of Leu15 decreased activity, but addition of Thr16 maintained good activity. The presence of hydrophobic residues appears to have a significant effect on the process of antibacterial activity. These peptide analogues showed voltage-dependent conductance changes and are capable of forming ion-pores in planar lipid bilayers. The antibacterial action of the peptides is thought to be first an ionic interaction with the anionic phosphate groups of the membrane followed by interaction with the hydrocarbon core of the membrane and subsequent reorientation into amphipathic alpha-helical peptides that form pores (ion-channels), which span the membrane. The analogue also showed an increase in alpha-helicity with an increase in hexafluoro 2-propanol concentration.

Amino Acid Sequence↗
PubMedDate not supplied

Immunogenicity studies with haptenated melittin peptides: implication for membrane involvement during the recognition step.

Melittin peptides carrying 2,4-dinitro-6-carboxyphenyl (Dncp) haptenic groups regularly evoked anti-hapten IgG responses in mice or guinea pigs when the hapten was C-terminally attached. Single haptens on the N-terminal helix in several positions gave poor or no responses in the early stages but adequate titres after prolonged immunization. Peptides with Dncp at the C-terminus as an invariant feature and a second Dncp in various positions along the peptide chain did not fail to produce adequate responses. The hampering effect is not due to a defect at the T-cell level but involves the recognition step on the B-cell. It is implied that the haptenic interaction with the paratope of the recognizing immunoglobulin on the B-cell involves the cell membrane in an important way. It is also suggested that late antibody responses should not be overlooked during the development of proteinaceous immunogens for vaccination.

Amino Acid Sequence↗
PubMed2003

Production and fragmentation of multiply charged ions in 'electron-free' matrix-assisted laser desorption/ionization.

An unusually large fraction of multiply charged ions is observed in 'electron-free' matrix-assisted laser desorption/ionization (MALDI). Here we investigate how the yield of multiply charged ions depends on experimental parameters in MALDI. It is found to increase if measures are taken to limit the number of electrons in the plume, for example, by using non-metallic MALDI targets or low laser pulse energies. The ionization energy of the matrix is another important parameter that affects the yield of multiply charged ions: matrices with high ionization energies lead to greater intensities of multiply charged ions. It is furthermore proposed that some of the fragment ions observed in MALDI are due to reactions of analyte with electrons in the plume. The possibility of electron capture dissociation of multiply charged ions produced by MALDI is shown.

Animals↗
PubMed1988

The determination of protein, oligonucleotide and peptide molecular weights by ion-spray mass spectrometry.

The mass spectra of several compounds with molecular weights in the 2500-20,000 Da range were obtained with a quadrupole mass spectrometer equipped with an atmospheric pressure ion source. Average molecular weight determinations of mellitin (2846.4 Da), a synthetic oligonucleotide (4262.8 Da), myoglobin (16,950.4 Da) and on the subunits of beta-lactoglobulin (18,277.1 Da) requiring as little as 1 pmol of material were achieved with accuracies and precisions of +/- 1 Da. An ion-spray interface was used to produce ions via the ion evaporation process, producing mass spectra containing a series of multiply-charged molecular species. A simple method for calculating the molecular weight of unknown compounds from the spectra containing multiply-charged ions is described.

Lactoglobulins↗
PubMed1992

Matrix-assisted laser desorption/ionization of high-mass molecules by Fourier-transform mass spectrometry.

Following the first demonstrations of high-mass analysis using time-of-flight matrix-assisted laser desorption/ionization (MALDI) techniques by Hillenkamp, Tanaka and their co-workers, there have been significant efforts in a number of laboratories to adapt the new methodology to Fourier-transform mass spectrometry (FTMS). The motivation for this research is obvious. Namely, it would be desirable to couple the unparalleled high mass resolution of FTMS with the extended mass range provided by MALDI, particularly for analysis of polymers and biomolecules. Unfortunately, prior to the present work, attempts to mate FTMS and MALDI have met with limited success. The highest mass matrix-assisted laser-desorption-FTMS result previously obtained appears to be the unpublished low resolution spectrum of bovine insulin recently reported by Russell and co-workers. We, Campana and co-workers, and Hettich and Buchanan have had some success with MALDI-FTMS of biomolecules with masses lower than 3000 Da, including melittin, a variety of lower mass peptides, and oligonucleotides with masses lower than 1800 Da. Furthermore, with the single exception of Campana's report of obtaining mass resolution of 5000 for the molecular ion of melittin, such spectra have not displayed high resolution. Here, we report successful development of MALDI-FTMS, demonstrated with spectra obtained from a variety of high-mass polymer and biomolecule samples, using 355 nm radiation from an excimer-pumped dye laser for desorption/ionization and sinapinic acid as matrix. Some of these spectra are of much higher mass resolution than is possible with current time-of flight mass spectrometers.

Animals↗