Publications by authors named "Daniela Meleleo"

19 Publications

  • Page 1 of 1

Study of Resveratrol's Interaction with Planar Lipid Models: Insights into Its Location in Lipid Bilayers.

Authors:
Daniela Meleleo

Membranes (Basel) 2021 Feb 14;11(2). Epub 2021 Feb 14.

Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro", via E. Orabona 4, 70126 Bari, Italy.

Resveratrol, a polyphenolic molecule found in edible fruits and vegetables, shows a wide range of beneficial effects on human health, including anti-microbial, anti-inflammatory, anti-cancer, and anti-aging properties. Due to its poor water solubility and high liposome-water partition coefficient, the biomembrane seems to be the main target of resveratrol, although the mode of interaction with membrane lipids and its location within the cell membrane are still unclear. In this study, using electrophysiological measurements, we study the interaction of resveratrol with planar lipid membranes (PLMs) of different composition. We found that resveratrol incorporates into palmitoyl-oleoyl-phosphatidylcholine (POPC) and POPC:Ch PLMs and forms conductive units unlike those found in dioleoyl-phosphatidylserine (DOPS):dioleoyl-phosphatidylethanolamine (DOPE) PLMs. The variation of the biophysical parameters of PLMs in the presence of resveratrol provides information on its location within a lipid double layer, thus contributing to an understanding of its mechanism of action.
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http://dx.doi.org/10.3390/membranes11020132DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7918209PMC
February 2021

Levels of Mercury, Methylmercury and Selenium in Fish: Insights into Children Food Safety.

Toxics 2021 Feb 20;9(2). Epub 2021 Feb 20.

Biosciences, Biotechnlogies and Biopharmaceutical Department, University of Bari "Aldo Moro", 70010 Valenzano, Bari, Italy.

Total mercury (THg), methylmercury (MeHg), and selenium (Se) concentrations were measured in various commercially important fish species. The benefit-risk binomial associated with these chemicals was assessed in children through the probability of exceeding the provisional tolerable weekly intakes (PTWIs) of the contaminants and the Se recommended dietary allowance (RDA). The Se:Hg molar ratios, selenium health benefit values (HBV), and monthly consumption rate limits (CR) for each species were also calculated. THg and Se were analyzed by atomic absorption spectrophotometer (Shimadzu, Milan, Italy), while MeHg was determined by Trace Ultra gas chromatograph connected with a PolarisQ MS (Thermo Fisher Scientific, Waltham, MA, USA). None of the analyzed fish had Hg levels above the European Community regulatory limits, while most large predators had MeHg levels over the threshold concentration set by US EPA. The estimated weekly intakes of THg and MeHg exceeded in many cases the PTWIs and the Se estimated daily intakes were provided from 0.71% to 2.75% of the RDA. Se:Hg molar ratios above 1 and positive HBV index suggested that Se in fish could be enough to alleviate the potential toxic effect of Hg. However, high-risk groups as children should consume fish in moderation because a large consumption pattern, especially of swordfish and tunas, might be of concern for health.
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http://dx.doi.org/10.3390/toxics9020039DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7923435PMC
February 2021

Trace Metals in Pork Meat Products Marketed in Italy: Occurrence and Health Risk Characterization.

Biol Trace Elem Res 2021 Aug 12;199(8):2826-2836. Epub 2020 Nov 12.

Biosciences, Biotechnology and Biopharmaceutical Department, University of Bari, Strada Prov.le per Casamassima Km 3, 70010, Valenzano (BA), Italy.

This study provides valuable information on the levels of various trace metals (Pb, Cd, Hg, Zn, Cu, Cr) in meat products (baked ham, raw ham, mortadella, cured sausage, würstel, salami) from South Italy and calculates potential health risk toxicity associated with their consumption for the total population and for children. In the samples studied metal concentrations are within the permissible legal limits (Cd: 0.01-0.03 μg g w.w., Hg: 0.01-0.02 μg g w.w., Zn: 5.71-7.32 μg g w.w., Cu: 1.08-1.21 μg g w.w., Cr: 0.15-0.23 μg g w.w.), except for Pb (Pb: 0.22-0.38 μg g w.w.). The estimated intake values are within the provisional tolerable daily intake limits for toxic metals and recommended daily intake values for essential metals in both tested groups. The noncarcinogenic risk values of the individual metals indicate that there is no health risk, but their combined effects might constitute a potential risk for children. Furthermore, the cumulative cancer risk of all samples studied exceeds the recommended threshold risk limit (> 10) in both total population and children, indicating a risk of potential health problems for consumers especially for children, who are more vulnerable to toxic metal exposure.
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http://dx.doi.org/10.1007/s12011-020-02417-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8222035PMC
August 2021

Evidence of cadmium and mercury involvement in the Aβ42 aggregation process.

Biophys Chem 2020 11 8;266:106453. Epub 2020 Aug 8.

Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro", via E. Orabona 4, 70126 Bari, Italy. Electronic address:

Aβ42 is a small peptide formed from 42 aminoacids that presents a great propensity to aggregate until it forms fibrils. Aβ42 aggregation and fibrillation are very complex processes whose molecular mechanisms seem to depend on characteristics intrinsic to the peptide molecule, as well as extrinsic factors. Peptide concentration, mean pH and several substances, including metal ions, are principal extrinsic factors for the oligomerization process. Different metals affect the aggregation of the Aβ42 molecule, and their toxicity favours the misfolding and aggregation of the peptide. In this study, we evaluate the effect of different concentrations of Cd and Hg on the Aβ42 peptide in solution by different methods. The toxicity of Aβ42 was evaluated with the MTT assay, while the aggregation process was monitored by single-channel measurements, electrophoresis and western blot. Cd and Hg seem to favour the formation of high-molecular-weight aggregates, to decrease ion channel turnover inside the membrane and to significantly increase Aβ42 toxicity.
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http://dx.doi.org/10.1016/j.bpc.2020.106453DOI Listing
November 2020

Concentration-dependent effects of mercury and lead on Aβ42: possible implications for Alzheimer's disease.

Eur Biophys J 2019 Mar 2;48(2):173-187. Epub 2019 Jan 2.

Department of Chemistry, University of Bari "Aldo Moro", via E. Orabona 4, 70126, Bari, Italy.

Mercury (Hg) and lead (Pb) are known to be toxic non-radioactive elements, with well-described neurotoxicology. Much evidence supports the implication of metals as potential risk cofactors in Alzheimer's disease (AD). Although the action mechanism of the two metals remains unclear, Hg and Pb toxicity in AD could depend on their ability to favour misfolding and aggregation of amyloid beta proteins (Aβs) that seem to have toxic properties, particularly in their aggregated state. In our study, we evaluated the effect of Hg and Pb both on the Aβ42 ion channel incorporated in a planar lipid membrane made up of phosphatidylcholine containing 30% cholesterol and on the secondary structure of Aβ42 in an aqueous environment. The effects of Hg and Pb on the Aβ42 peptide were observed for its channel incorporated into a membrane as well as for the peptide in solution. A decreasing Aβ42 channel frequency and the formation of large and amorphous aggregates in solution that are prone to precipitate were both dependent on metal concentration. These experimental data suggest that Hg and Pb interact directly with Aβs, strengthening the hypothesis that the two metals may be a risk factor in AD.
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http://dx.doi.org/10.1007/s00249-018-1344-9DOI Listing
March 2019

Effect of calcium ions on human calcitonin. Possible implications for bone resorption by osteoclasts.

Biometals 2016 Feb 23;29(1):61-79. Epub 2015 Nov 23.

Interateneo di Fisica, University of Bari "Aldo Moro", via E. Orabona 4, 70126, Bari, Italy.

Calcium ions (Ca(2+)) are indispensable for life and are involved in important physiological actions, which makes maintaining a constant level of blood Ca(2+) essential. Ca(2+) is mainly stored in bones which serve as a reservoir and its homeostasis is modulated by various hormones. Human calcitonin (hCt) is a small peptide hormone that exerts its physiological effect on Ca(2+) metabolism by means of osteoclast-mediated bone resorption inhibition. Most of these actions are mediated through peptide/receptor interaction that acts via a second messenger. However, in vitro studies have shown that hCt can interact with membrane lipids to form ion channels in membrane models. This ability is due to the peptide's secondary structure and aggregation state, that can be modulated by different molecules. In our study, we evaluated the effect of Ca(2+), at different concentrations, both on the hCt ion channel incorporated into a planar lipid membrane made up of phosphatidylcholine containing 15% phosphatidylglycerol and on the secondary structure of hCt in an aqueous environment. Ca(2+) is able to interact with the hCt peptide by acting on the channel incorporated into the membrane as well as on the peptide in solution, both by increasing hCt channel frequency and in solution promoting α-helix formation, that counteracts the fibrillating process. These experimental observations, suggesting that hCt senses Ca(2+) concentration variations, strengthen the hypothesis that channel formation represents an extra source of Ca(2+) entry into osteoclasts in addition to the well-known interaction of the monomer with the specific receptor.
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http://dx.doi.org/10.1007/s10534-015-9896-yDOI Listing
February 2016

Heavy metals toxicity: effect of cadmium ions on amyloid beta protein 1-42. Possible implications for Alzheimer's disease.

Biometals 2014 Apr 21;27(2):371-88. Epub 2014 Feb 21.

Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro", via E. Orabona 4, 70126, Bari, Italy.

Cadmium (Cd) is an environmental contaminant, highly toxic to humans. This biologically non-essential element accumulates in the body, especially in the kidney, liver, lung and brain and can induce several toxic effects, depending on the concentration and the exposure time. Cd has been linked to Alzheimer's disease (AD) as a probable risk factor, as it shows higher concentrations in brain tissues of AD patients than in healthy people, its implication in the formation of neurofibrillary tangles and in the aggregation process of amyloid beta peptides (AβPs). AβPs seem to have toxic properties, particularly in their aggregated state; insoluble AβP forms, such as small and large aggregates, protofibrils and fibrils, appear to be implicated in the pathogenesis of AD. In our study, we have evaluated the effect of Cd, at different concentrations, both on the AβP1-42 ion channel incorporated in a planar lipid membrane made up of phosphatidylcholine containing 30 % cholesterol and on the secondary structure of AβP1-42 in aqueous environment. Cadmium is able to interact with the AβP1-42 peptide by acting on the channel incorporated into the membrane as well as on the peptide in solution, both decreasing AβP1-42 channel frequency and in solution forming large and amorphous aggregates prone to precipitate. These experimental observations suggesting a toxic role for Cd strengthen the hypothesis that Cd may interact directly with AβPs and may be a risk factor in AD.
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http://dx.doi.org/10.1007/s10534-014-9719-6DOI Listing
April 2014

AβP1-42 incorporation and channel formation in planar lipid membranes: the role of cholesterol and its oxidation products.

J Bioenerg Biomembr 2013 Aug 26;45(4):369-81. Epub 2013 Apr 26.

Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro", Via E. Orabona 4, 70126 Bari, Italy.

Amyloid beta peptide (AβP) is a natural peptide, normally released into the cerebrospinal fluid (CSF), that plays a key role in Alzheimer's disease. The conversion of the peptide from a native soluble form to a non-native and often insoluble form, such as small and large aggregates, protofibrils and fibrils of AβP appears to be implicated in the pathogenesis of AD. Although the molecular mechanisms of AβP neurotoxicity are not fully understood, a large body of data suggests that the primary target of amyloid peptides is the cell membrane of neurons, that may modulate the structural and functional conversion of AβP into assemblies involved in pathological processes. In our study, we provide a systematic investigation of AβP1-42's ability to incorporate and form channel-like events in membranes of different lipid composition and focus on cholesterol and its oxidation products. We propose that cholesterol and its oxidation products can be considered neuroprotective factors because a) by favouring AβP1-42 insertion into membranes, the fibrillation/clearance balance shifts toward clearance; b) by shifting channel selectivity toward anions, the membrane potential is moved far from the threshold of membrane excitability, thus decreasing the influx of calcium into the cell.
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http://dx.doi.org/10.1007/s10863-013-9513-0DOI Listing
August 2013

Choline modulation of the aβ p1-40 channel reconstituted into a model lipid membrane.

Int J Alzheimers Dis 2011 Jan 3;2010:752804. Epub 2011 Jan 3.

Dipartimento Farmaco-Biologico, Università degli Studi di Bari, Via E. Orabona 4, 70126 Bari, Italy.

Nicotinic acetylcholine receptors (AChRs), implicated in memory and learning, in subjects affected by Alzheimer's disease result altered. Stimulation of α7-nAChRs inhibits amyloid plaques and increases ACh release. β-amyloid peptide (AβP) forms ion channels in the cell and model phospholipid membranes that are retained responsible in Alzheimer disease. We tested if choline, precursor of ACh, could affect the AβP1-40 channels in oxidized cholesterol (OxCh) and in palmitoyl-oleoyl-phosphatidylcholine (POPC):Ch lipid bilayers. Choline concentrations of 5 × 10(-11) M-1.5 × 10(-8) M added to the cis- or trans-side of membrane quickly increased AβP1-40 ion channel frequency (events/min) and ion conductance in OxCh membranes, but not in POPC:Ch membranes. Circular Dichroism (CD) spectroscopy shows that after 24 and 48 hours of incubation with AβP1-40, choline stabilizes the random coil conformation of the peptide, making it less prone to fibrillate. These actions seem to be specific in that ACh is ineffective either in solution or on AβP1-40 channel incorporated into PLMs.
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http://dx.doi.org/10.4061/2010/752804DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3022179PMC
January 2011

Kissper, a kiwi fruit peptide with channel-like activity: structural and functional features.

J Pept Sci 2008 Jun;14(6):742-54

Istituto di Biochimica delle Proteine, CNR, Napoli, Italy.

Kissper is a 39-residue peptide isolated from kiwi fruit (Actinidia deliciosa). Its primary structure, elucidated by direct protein sequencing, is identical to the N-terminal region of kiwellin, a recently reported kiwi fruit allergenic protein, suggesting that kissper derives from the in vivo processing of kiwellin. The peptide does not show high sequence identity with any other polypeptide of known function. However, it displays a pattern of cysteines similar, but not identical, to those observed in some plant and animal proteins, including toxins involved in defence mechanisms. A number of these proteins are also active on mammalian cells. Functional characterization of kissper showed pH-dependent and voltage-gated pore-forming activity, together with anion selectivity and channeling in model synthetic PLMs, made up of POPC and of DOPS:DOPE:POPC. A 2DNMR analysis indicates that in aqueous solution kissper has only short regions of regular secondary structure, without any evident similarity with other bioactive peptides. Comparative analysis of the structural and functional features suggests that kissper is a member of a new class of pore-forming peptides with potential effects on human health.
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http://dx.doi.org/10.1002/psc.992DOI Listing
June 2008

Frog intestinal sac as an in vitro method for the assessment of intestinal permeability in humans: Application to carrier transported drugs.

Int J Pharm 2008 Mar 11;352(1-2):182-8. Epub 2007 Dec 11.

Dipartimento Farmaco-Chimico, Facoltà di Farmacia, Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy.

The aim of this study was to investigate the presence of pharmaceutically relevant drug transporters in frog intestine which has been proposed as model for intestinal permeability screening assays of passively absorbed drugs in humans [Trapani, G., Franco, M., Trapani, A., Lopedota, A., Latrofa, A., Gallucci, E., Micelli, S., Liso, G., 2004. Frog intestinal sac: a new in vitro method for the assessment of intestinal permeability. J. Pharm. Sci. 93, 2909-2919]. The expression of transporters in frog intestine was supported by the following observations: (i) the involvement of purine nucleobase transport system was deduced by inhibition of acyclovir transport in the presence of adenine; (ii) baclofen or l-dopa transport was inhibited by the digitalis steroid ouabain and it may be related to the Na(+) electrochemical potential difference, presumably involving amino acid transporters; (iii) the presence of proton-dependent peptide transporters was argued evaluating the effect of the pH change (from pH 5.9 to pH 7.4) on the transport of glutathione; (iv) the possible expression in the frog intestine of an efflux system distinct from P-glycoprotein (Pgp) in the benzylpenicillin transport was deduced using a glucose enriched frog Ringer with or without the known Pgp inhibitor verapamil; (v) the contribution of Pgp-mediated efflux system in determining the frog intestinal absorption of drugs was supported by the specific inhibition of cimetidine or nadolol transport in the presence of verapamil. These results indicate that pharmaceutically relevant drug transporters should be also expressed in frog intestine. In this work, an attempt was also made to compare the measured P(app) values in the frog intestinal model for the aforementioned series of actively/effluxed transported drugs in humans to the corresponding literature values for the fraction absorbed. The P(app) values used in these comparisons were obtained at high concentrations of drugs at which probably saturation of the carrier occurs. Interestingly, it was found that drugs that are completely absorbed had P(app) values >3 x 10(-6)cm/s, while drugs absorbed <90% had P(app) values lower than 1 x 10(-6)cm/s. In these cases, indeed, a borderline region characterized by the apparent permeability coefficient P(app) value between 1 x 10(-6) and 3 x 10(-6)cm/s should be considered for which the prediction of the absorbed fraction after oral administration in humans become more uncertain by the frog intestinal sac system.
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http://dx.doi.org/10.1016/j.ijpharm.2007.10.027DOI Listing
March 2008

Acetyl-[Asn30,Tyr32]-calcitonin fragment 8-32 forms channels in phospholipid planar lipid membranes.

Eur Biophys J 2007 Sep 29;36(7):763-70. Epub 2007 Mar 29.

Dipartimento Farmaco-Biologico, Università degli Studi di Bari, Bari, Italy.

The N-terminally truncated derivative of salmon calcitonin (sCt) (acetyl-[Asn(30),Tyr(32)]-calcitonin fragment 8-32) (AC 187) lacks hormonal activity and is a potent and selective antagonist of the hormone and amylin receptor. It was investigated for its capability to interact and form channels in palmitoleoylphosphatidylcholine:dioleoylphosphatidylglycerol planar lipid membranes. Interestingly, AC 187 exhibits channel activity, whose parameters, i.e., central conductance (Lambda (c)), occurrence (number of channels/min), voltage-dependence and lifetime, are similar to those found for sCt although, in the same experimental conditions, it takes longer to incorporate into the membrane than sCt. This channel activity can be modulated by changing either the holding potential or the pH of the medium, or by adding picomolar concentrations of SDS. One evident difference between the two peptides is that sCt is unselective (1.03) while AC 187 displays a cationic selectivity (P (K) (+)/P (Cl) (-) = 2.7) at pH 7, increasing to 3.87 when the pH drops to 3.8. The present findings indicate that the 1-7 disulfide bridge is sufficient but not necessary for membrane interaction, in accordance with the observation reported on the interaction with membrane receptors. Furthermore, the remarkable pH dependence of the cationic channel could be taken into consideration for full biotechnological study.
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http://dx.doi.org/10.1007/s00249-007-0150-6DOI Listing
September 2007

Water permeability of rat liver mitochondria: A biophysical study.

Biochim Biophys Acta 2006 Aug 21;1758(8):1018-24. Epub 2006 Jul 21.

Dipartimento di Fisiologia Generale ed Ambientale and Centro di Eccellenza di Genomica in campo Biomedico ed Agrario (CEGBA), Università degli Studi di Bari, Via Amendola 165/A, 70126 Bari, Italy.

The movement of water accompanying solutes between the cytoplasm and the mitochondrial spaces is central for mitochondrial volume homeostasis, an important function for mitochondrial activities and for preventing the deleterious effects of excess matrix swelling or contraction. While the discovery of aquaporin water channels in the inner mitochondrial membrane provided valuable insights into the basis of mitochondrial plasticity, questions regarding the identity of mitochondrial water permeability and its regulatory mechanism remain open. Here, we use a stopped flow light scattering approach to define the water permeability and Arrhenius activation energy of the rat liver whole intact mitochondrion and its membrane subcompartments. The water permeabilities of whole brain and testis mitochondria as well as liposome models of the lipid bilayer composing the liver inner mitochondrial membrane are also characterized. Besides finding remarkably high water permeabilities for both mitochondria and their membrane subcompartments, the existence of additional pathways of water movement other than aquaporins are suggested.
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http://dx.doi.org/10.1016/j.bbamem.2006.07.008DOI Listing
August 2006

Effect of pH-variation on insertion and ion channel formation of human calcitonin into planar lipid bilayers.

Front Biosci 2006 Sep 1;11:2035-44. Epub 2006 Sep 1.

Dept. Farmaco-Biologico, Università degli Studi di Bari, I-70126 Bari, Italy.

Human calcitonin is the physiological hormone involved in calcium-phosphorus homeostasis. However, its use is limited by its propensity to form aggregates. We find that the type of host lipid has a pronounced influence on human calcitonin fibrillation or incorporation, as assessed by channel formation, in planar lipid membranes at neutral pH. At pH 7, human calcitonin is able to interact and form channels with negatively charged dioleoyl-phosphatidylglycerol (DOPG) bilayers and with zwitterionic palmitoyl-oleoyl phosphatidylcholine (POPC) bilayers containing 15% negatively-charged DOPG, but not with POPC bilayers. At low pH (4.5 and 3.8), the conformational variation of the peptide enables it to insert into POPC and POPC:DOPG but not into DOPG bilayers. The model proposed for human calcitonin interaction and channel formation at acidic pH was based on theoretical predictions of the protonation-deprotonation state of some amino acids, in particular in the fibrillating sequence of peptide molecules; the length of the alpha-helix, and the electrostatic and/or hydrophobic interaction also seem to be relevant. These results may suggest that human calcitonin at low local pH could be involved in osteoclasts' calcium-sensitive permeability through channel formation and/or receptor interaction.
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http://dx.doi.org/10.2741/1945DOI Listing
September 2006

Effect of eel calcitonin glycosylation on incorporation and channel formation in planar phospholipid membranes.

Peptides 2006 Apr 11;27(4):805-11. Epub 2005 Nov 11.

Dipartimento Farmaco-Biologico, Università degli Studi di Bari, I-70126 Bari, Italy.

Previous studies have shown that different calcitonins interact with planar lipid membranes to form ion channels. In this study, glycosylation of eel calcitonin (eCt) at different positions (Ct3-GlcNAc, Ct14-GlcNAc, Ct20-GlcNAc, Ct26-GlcNAc) is shown to preserve molecular structure and slightly change the energy of incorporation and channel formation in planar lipid bilayers made up of palmitoyl-oleoyl-phosphatidylcholine:dioleoyl phosphatidyl-glycerol (85:15, w:w). The voltage needed to form channels decreased as the attached carbohydrate moved toward the C-terminal (eCt = Ct3-GlcNAc > Ct14-GlcNAc = Ct20-GlcNAc > Ct26-GlcNAc). Interestingly, all the Cts tested maintain the characteristic voltage-conductance dependence found for other Cts, the only channel properties modified concern ion selectivity, that shift toward anion selectivity (eCt = 0.97, Ct3-GlcNAc = 0.49, Ct14-GlcNAc = 0.41, Ct20-GlcNAc = 0.36, Ct26-GlcNAc = 0.47). These aspects would be useful in managing peptide properties for biotechnological and therapeutic applications considering the physiological nature of this peptide.
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http://dx.doi.org/10.1016/j.peptides.2005.09.011DOI Listing
April 2006

Effect of nanomolar concentrations of sodium dodecyl sulfate, a catalytic inductor of alpha-helices, on human calcitonin incorporation and channel formation in planar lipid membranes.

Biophys J 2004 Aug;87(2):1065-75

Dipartimento Farmaco-Biologico, Dipartimento Interateneo di Fisica, Università degli Studi di Bari, I-70126 Bari, Italy.

Human Calcitonin (hCt) is a peptide hormone which has a regulatory action in calcium-phosphorus metabolism. It is currently used as a therapeutic tool in bone pathologies such as osteoporosis and Paget's disease. However, due to its amphiphilic property tends to form a gelatinous solution in water which consists of fibrils that limits its therapeutic use. Here we show that sodium dodecyl sulfate (SDS), an anionic detergent able to induce and stabilize alpha-helices in polypeptides, at a monomeric concentration ranging between 0.26 mM-5 pM (all concentrations are below the CMC), increases the rate and number of hCt channel formation in planar lipid membranes, at both high and low hCt concentrations, with a maximum increase at a molecular hCt/SDS ratio of 1000:1. This effect could be interpreted as a counteraction to the fibrillation process of hCt molecules by removing molecules available for aggregation from the fluid; furthermore, this action, independently of channel formation in the cell membrane, could improve the peptide-receptor interaction. The action of SDS could be attributable to the strength of the sulfate negative charge and the hydrophobic chain; in fact, a similar effect was obtained with lauryl sarcosine and not with a neutral detergent such as n-dodecyl-beta-D-maltoside. The very low molecular ratio between SDS and peptide is suggestive of a possible catalytic action of SDS that could induce alpha-helices, the appropriate structures for interacting with the membrane. Moreover, in the experimental conditions investigated, the addition of SDS does not modify the membrane's electrical properties and most of the channel properties. This finding may contribute to the knowledge of environment-folding diseases due to protein and peptides.
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http://dx.doi.org/10.1529/biophysj.103.037200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1304447PMC
August 2004

Effect of sterols on beta-amyloid peptide (AbetaP 1-40) channel formation and their properties in planar lipid membranes.

Biophys J 2004 Apr;86(4):2231-7

Dipartimento Farmaco-Biologico, Università degli Studi di Bari, 70126 Bari, Italy.

We investigate the role played by membrane composition on the interaction and self-assembly of beta-amyloid peptide (AbetaP1-40) during pore formation in planar lipid membranes (PLMs). Incorporation studies showed that AbetaP does not interact with zwitterionic membranes made up of phosphatidylcholine, whereas the addition of cholesterol or ergosterol to the membranes leads to channel formation. Among the PLMs used, a higher propensity of AbetaP to form channels at low applied potential (+/-20 mV) was observed in 7-dehydrocholesterol and in oxidized cholesterol PLMs. These channels present long lifetimes, high-occurrence frequencies, and are voltage dependent. In particular, the AbetaP channel in oxidized cholesterol showed anion selectivity. Thus cholesterol (and sterols in general) could be considered as targets for AbetaP, which prevents the fibrillation process by increasing incorporation into membranes. Furthermore, by switching the channel selectivity versus anions, cholesterol helps to reduce the imbalance of the cellular ions, calcium included, induced by membrane depolarization, which could be one of the factors responsible for cytotoxicity in Alzheimer's disease.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1304073PMC
http://dx.doi.org/10.1016/S0006-3495(04)74281-2DOI Listing
April 2004

Magainin 2 channel formation in planar lipid membranes: the role of lipid polar groups and ergosterol.

Eur Biophys J 2003 Mar 22;32(1):22-32. Epub 2002 Nov 22.

Dipartimento Farmaco-Biologico, Università degli Studi di Bari, 70126 Bari, Italy.

Magainin 2, a polycationic peptide, displays bactericidal and tumoricidal activity, presumably interacting with negatively charged phospholipids in the membrane hosts. In this work, we investigate the role played by the lipid head-group in the interactions and self-association of magainin 2 during pore formation in lipid bilayers. Two methods are used: single-channel and macroscopic incorporation into planar lipid membranes. Single-channel incorporation showed that magainin 2 did not interact with zwitterionic membranes, while the addition of negatively charged dioleoylphosphatidylglycerol to the membrane leads to channel formation. On the other hand, magainin 2 did not form channels in membranes made up of dioleoylphosphatidylserine (DOPS), although the addition of ergosterol to DOPS membranes leads to channel formation. This finding could indicate that ergosterol may be a possible target of magainin 2 in fungal membranes. Further support for this hypothesis comes from experiments in which the addition of ergosterol to palmitoyloleoylphosphatidylcholine membranes induced channel formation. Besides the role of negatively charged membranes, this study has shown that magainin 2 also forms channels in membranes lacking heads, such as monoolein and oxidized cholesterol, indicating an interaction of magainin 2 with acyl chains and cholesterol, respectively. This finding provides further evidence that peptide binding and assembly in lipid membranes is a complex process driven by electrostatic and/or hydrophobic interactions, depending on the structure of the peptide and the membrane composition.
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http://dx.doi.org/10.1007/s00249-002-0262-yDOI Listing
March 2003

Mitochondrial porin incorporation into black lipid membranes: ionic and gating contribution to the total current.

Bioelectrochemistry 2002 Sep;57(2):97-106

Dipartimento Farmaco-Biologico, Facoltà di Farmacia, Università degli Studi di Bari, v.E. Orabona 4, 70125, Bari, Italy.

We present a new ac device useful for simultaneous measurements of ionic charge movement (conductance) and gating charge displacement (capacitance) in mitochondrial porin channels incorporated in two kinds of black lipid membranes (BLMs), made up of phosphatidylinositol (charged surface) and oxidized cholesterol (neutral surface). In particular, we investigated the conductance/capacitance variations during the process of porin incorporation (VDAC) at different porin concentrations. While conductance variations are present throughout the porin concentration range investigated, a threshold value seems to be necessary in order to detect a significant capacitance variation. A clear steady state in both conductance and capacitance is reached for the phosphatidylinositol bilayer, while for the oxidized cholesterol membranes, the steady state is reached only for the conductance. The dependence of capacitance characteristics on the membrane applied voltage V(m) is investigated before porin incorporation and at the ionic current steady state. The results obtained confirm that before porin incorporation, there is a small dependence on V(m)(2), while afterwards we find evidence of a dual exponential voltage dependence (a result similar to that found for conductance). Finally, we investigated the capacitance dependence on the radius of the hole separating the two compartments of the cell used in the measurements. In this study, performed only with oxidized cholesterol, the radius was varied from 200 to 1050 microm. We observed a significant variation in the specific capacitance in particular for smaller radii. The results were interpreted by a simple geometrical model taking into account the influence of the torus.
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http://dx.doi.org/10.1016/s1567-5394(02)00003-8DOI Listing
September 2002
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