Free energy barrier for melittin reorientation from a membrane-bound state to a transmembrane state

An important step in a phospholipid membrane pore formation by melittin antimicrobial peptide is a reorientation of the peptide from a surface into a transmembrane conformation. In this work we perform umbrella sampling simulations to calculate the potential of mean force (PMF) for the reorientation of melittin from a surface-bound state to a transmembrane state and provide a molecular level insight into understanding peptide and lipid properties that influence the existence of the free energy barrier. The PMFs were calculated for a peptide to lipid (P/L) ratio of 1/128 and 4/128. We observe that the free energy barrier is reduced when the P/L ratio increased. In addition, we study the cooperative effect; specifically we investigate if the barrier is smaller for a second melittin reorientation, given that another neighboring melittin was already in the transmembrane state. We observe that indeed the barrier of the PMF curve is reduced in this case, thus confirming the presence of a cooperative effect

Side Chain Hydrophobicity Modulates Therapeutic Activity and Membrane Selectivity of Antimicrobial Peptide Mastoparan-X

The discovery of new anti-infective compounds is stagnating and multi-resistant bacteria continue to emerge, threatening to end the "antibiotic era". Antimicrobial peptides (AMPs) and lipo-peptides such as daptomycin offer themselves as a new potential class of antibiotics; however, further optimization is needed if AMPs are to find broad use as antibiotics. In the present work, eight analogues of mastoparan-X (MPX) were investigated, having side chain modifications in position 1, 8 and 14 to modulate peptide hydrophobicity. The self-association properties of the peptides were characterized, and the peptide-membrane interactions in model membranes were compared with the bactericidal and haemolytic properties. Alanine substitution at position 1 and 14 resulted in higher target selectivity (red blood cells versus bacteria), but also decreased bactericidal potency. For these analogues, the gain in target selectivity correlated to biophysical parameters showing an increased effective charge and reduction in the partitioning coefficient for membrane insertion. Introduction of an unnatural amino acid, with an octyl side chain by amino acid substitution, at positions 1, 8 and 14 resulted in increased bactericidal potency at the expense of radically reduced membrane target selectivity. Overall, optimized membrane selectivity or bactericidal potency was achieved by changes in side chain hydrophobicity of MPX. However, enhanced potency was achieved at the expense of selectivity and vice versa in all cases

Panethnic Differences in Blood Pressure in Europe: A Systematic Review and Meta-Analysis

BACKGROUND: People of Sub Saharan Africa (SSA) and South Asians(SA) ethnic minorities living in Europe have higher risk of stroke than native Europeans(EU). Study objective is to provide an assessment of gender specific absolute differences in office systolic(SBP) and diastolic(DBP) blood pressure(BP) levels between SSA, SA, and EU. METHODS AND FINDINGS: We performed a systematic review and meta-analysis of observational studies conducted in Europe that examined BP in non-selected adult SSA, SA and EU subjects. Medline, PubMed, Embase, Web of Science, and Scopus were searched from their inception through January 31st 2015, for relevant articles. Outcome measures were mean SBP and DBP differences between minorities and EU, using a random effects model and tested for heterogeneity. Twenty-one studies involving 9,070 SSA, 18,421 SA, and 130,380 EU were included. Compared with EU, SSA had higher values of both SBP (3.38 mmHg, 95% CI 1.28 to 5.48 mmHg; and 6.00 mmHg, 95% CI 2.22 to 9.78 in men and women respectively) and DBP (3.29 mmHg, 95% CI 1.80 to 4.78; 5.35 mmHg, 95% CI 3.04 to 7.66). SA had lower SBP than EU(-4.57 mmHg, 95% CI -6.20 to -2.93; -2.97 mmHg, 95% CI -5.45 to -0.49) but similar DBP values. Meta-analysis by subgroup showed that SA originating from countries where Islam is the main religion had lower SBP and DBP values than EU. In multivariate meta-regression analyses, SBP difference between minorities and EU populations, was influenced by panethnicity and diabetes prevalence. CONCLUSIONS: 1) The higher BP in SSA is maintained over decades, suggesting limited efficacy of prevention strategies in such group in Europe;2) The lower BP in Muslim populations suggests that yet untapped lifestyle and behavioral habits may reveal advantages towards the development of hypertension;3) The additive effect of diabetes, emphasizes the need of new strategies for the control of hypertension in groups at high prevalence of diabetes

Thermodynamics of Melittin Binding to Lipid Bilayers : aggregation/Pore Formation

Lipid membranes act as catalysts for protein folding. Both alpha-helical and beta-sheet structures can be induced by the interaction of peptides or proteins with lipid surfaces. Melittin, the main component of bee venom is a particularly well-studied example for the membrane-induced random coil-to-?-helix transition. Melittin in water adopts essentially a random coil conformation. The cationic amphipathic molecule has a high affinity for neutral and anionic lipid membranes and exhibits about 50-65% ?-helix conformation in the membrane-bound state. At higher melittin concentrations, the peptide forms aggregates/pores in the membrane. In spite of the long-standing interest in melittin-lipid interactions no systematic thermodynamic study is available. This is probably caused by the complexity of the binding process. Melittin binding to lipid vesicles is fast and occurs within milliseconds but the binding process involves at least 4 steps, namely (i) the electrostatic attraction of the cationic peptide to an anionic membrane surface, (ii) the hydrophobic insertion into the lipid membrane, (iii) the conformational change from random coil to ?-helix and (iv) peptide aggregation in the lipid phase. We have combined microelectrophoresis (measurement of the ?-potential), isothermal titration calorimetry, and circular dichroism spectroscopy to provide a thermodynamic analysis of the individual binding steps. We have compared melittin with a synthetic analog, [D]-V5,8,I17,K21-melittin where ?-helix formation is suppressed and replaced by ?-structure formation. The comparison reveals that the thermodynamic parameters for the membrane-induced ?-helix formation of melittin are identical to those observed earlier for other peptides with an enthalpy hhelix = -0.7 kcal/mol and a free energy of ghelix = -0.2 kcal/mol per peptide residue. These thermodynamic parameters hence appear to be of general validity for lipid-induced membrane folding. As g(helix) is negative, it further follows that helix formation leads to an enhanced membrane binding for the peptides or proteins involved. In this study, melittin binds by approximately 2 orders of magnitude better to the lipid membrane than [D]-V(5,8),I(17),K(21)-melittin which cannot form an alpha-helix. We also found conditions under which the isothermal titration experiment reports only the aggregation process. Melittin aggregation is an entropy-driven process with an endothermic heat of reaction (DeltaH(agg)) of approximately 2 kcal/mol and an aggregation constant of 20-40 M(-1)

Preparation and Characterization of Rare Earth Doped Fluoride Nanoparticles

This paper reviews the synthesis, structure and applications of metal fluoride nanoparticles, with particular focus on rare earth (RE) doped fluoride nanoparticles obtained by our research group. Nanoparticles were produced by precipitation methods using the ligand ammonium di-n-octadecyldithiophosphate (ADDP) that allows the growth of shells around a core particle while simultaneously avoiding particle aggregation. Nanoparticles were characterized on their structure, morphology, and luminescent properties. We discuss the synthesis, properties, and application of heavy metal fluorides; specifically LaF3:RE and PbF2, and group IIA fluorides. Particular attention is given to the synthesis of core/shell nanoparticles, including selectively RE-doped LaF3/LaF3, and CaF2/CaF2 core/(multi-)shell nanoparticles, and the CaF2-LaF3 system

IDENTIFICATION OF THE HEMODYNAMIC MODULATORS (VOLEMIA, INOTROPY AND VASOACTIVITY) AND HEMODYNAMIC STATUS IN UNCONTROLLED HYPERTENSIVE PATIENTS

Introduction: Despite of the progress of antihypertensive drug treatment, only 20–30% out of the treated patients are achieving blood pressure control. These poor results could be partially due to the fact that doctors are having no possibilities to detect which is the hemodynamic cause of the hypertension (hypervolemia, hyperinotropy or vasoconstriction). Under these circumstances, blood pressure problem is treated like a symptom and selection of antihypertensive agents is often done independently of the hemodynamic profile of the patient. Objective: Identification of the hemodynamic modulators (volemia, inotropy and vasoactivity) and hemodynamic status (MAP and SI) in uncontrolled hypertensive patients. Methods: We enrolled in 9 centers 114 uncontrolled hypertensive patients with essential hypertension treated with at least 2 antihypertensive drugs. We implemented HOTMAN® system for noninvasive assessment of hemodynamic modulators and evaluation of the hemodynamic status of the patients. Results: Office systolic and diastolic BP averaged 156/92 mmHg. Among the whole study group 59 (51.7%) were diagnosed as normodynamic while 33 (29%) as hypodynamic and 22 (19.3%) as hyperdynamic. Modulators Distribution: One abnormal hemodynamic modulator for 35 (30.7%) patients, two for 22 (19.3) patients and three for 52 (45.6%) patients. Different combinations of hemodynamic modulators were present, the most common being concomitant hypervolemia, hypoinotropy and vasoconstriction – in 46 (40.3%) patients. Antihypertensive drug distribution in this subgroup: 89.1% used diuretics, 30.4% – vasodilator beta-blockers, 21.7% – nonvasodilator beta-blockers, 23.9% – ACEI, 73.9% – ARB, 73.9% – dihydropyridine CCB. Two hemodynamic states correspond to this subgroup: hypodynamic 31 (67.3%) patients and normodynamic 15 (32%) patients. Conclusion: Data suggest there is a strong relation between hypertension and abnormal hemodynamic modulators. Careful analysis of all hemodynamic modulators should precede pharmacological treatment modification in order to achieve a normohemodynamic status. The clinical benefits potentially offered by a larger use of this technique in the daily management of patients would require to be tested by future longitudinal outcome studies