Interactions of an Anionic Antimicrobial Peptide with Zinc(II): Application to Bacterial Mimetic Membranes

While the majority of known antimicrobial peptides are cationic, a small number consist of short Asp-rich sequences that are anionic. These require metal ions to become biologically active. Here, we report the study of the zinc complexes of the peptide GADDDDD (GAD5), an antimicrobial peptide. Using a combination of dynamic light scattering (DLS), ζ-potential, infrared, Raman, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), we find that adding zinc ions to GAD5 forces it into a compact structure. Higher amounts of zinc ions favor a larger structure, possibly a dimer. SEM images show that zinc ions reduce the size of the fibrillar structures of GAD5. TGA curves show that the addition of zinc ions increases the thermal stability of the structure of the peptide. TGA and DSC indicate that the association of GAD5 with a zwitterionic phospholipid in the presence of zinc ions is the most stable. The stability of that complex is due to the presence of a sharp endothermic peak in the 200-300 °C range, suggesting the presence of interlamellar water that is essential to the stabilization of the structure. These results indicate that the Zn-GAD5 complex prefers the bacteria-mimicking neutral (zwitterionic) membranes. In the presence of negatively charged phospholipids, the complex remains unordered and unstable. In terms of mechanism of action, the Zn-GAD5 complex promotes a possible endocytic uptake with respect to neutral (zwitterionic) membranes while promoting membrane disruption by forming pores with respect to negatively charged phospholipids.

Vesicles mimicking normal and cancer cell membranes exhibit differential responses to the cell-penetrating peptide Pep-1

The cell-penetrating peptide (CPP) Pep-1 presents a great potential in drug delivery due to its intrinsic property to cross plasma membrane. However, its mechanism of entry into the cell remains unresolved. In this study, we compare the selectivity of Pep-1 towards vesicles mimicking normal and cancer cell membranes. The interaction was performed in a wide range of peptide-to-lipid molar ratios using infrared (IR), fluorescence, scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. At low peptide concentration, fluorescence experiments show that lipid-phosphatidylserine (PS) seems to enable Pep-1 translocation into cancer cell membrane as evidenced by the blue shift of its maximal emission wavelength. DSC data show that Pep-1 induces segregation of lipids. At high peptide concentration, IR data indicate that the interaction of Pep-1 is relatively stronger with normal cell membrane than with cancer cell membrane through the phosphate groups, while the interaction is weaker with normal cell membrane than with cancer cell membrane through the carbonyl groups. TGA and DSC data reveal that vesicles of normal cell membrane are thermally more stable than vesicles of cancer cell membrane. This suggests that the additional lipid PS included in cancer cell membrane has a destabilizing effect on the membrane structure. SEM images reveal that Pep-1 form superstructures including spherical particles and fibrils in the presence of both model membranes. PS seems to enhance peptide transport across cellular membranes. The biophysical techniques in this study provide valuable insights into the properties of CPPs in drug delivery systems.

Calorimetric and Spectroscopic Studies of the Effects of the Cell Penetrating Peptide Pep-1 and the Antimicrobial Peptide Combi-2 on Vesicles Mimicking Escherichia coli Membrane

The objective of this study is to measure and compare the effects of the cell penetrating peptide (CPP) Pep-1 and the antimicrobial peptide (AMP) combi-2 on vesicles of membranes mimicking Escherichia coli (E. coli). To characterize the effects of Pep-1 and combi-2 on E. coli membrane vesicles, a combination of five biophysical techniques was employed: fluorescence, infrared, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) techniques. Upon addition of E. coli membranes, tryptophan fluorescence intensity of Pep-1 showed a sudden blue-shift and decreased in a nonconcentration-dependent manner while the intensity of combi-2 decreased in a concentration-dependent manner, most significantly for a very low peptide-to-lipid ratio of 1:40. Complexes of Pep-1 and combi-2 with E. coli membrane mimicking vesicles having shown a significant blue-shift in fluorescence intensity were then prepared and studied in freeze-dried states. IR results indicate that Pep-1 and combi-2 adopt a major 3₁₀-helix structure in the presence of E. coli membrane mimicking vesicles at low peptide concentration. Pep-1 and combi-2 have a similar effect on E. coli membrane mimicking vesicles at low concentration even though combi-2 is in the interfacial region of the bilayer while Pep-1 is located between the interfacial region and the hydrophobic region. Combi-2 at low concentration acts as a CPP. TGA and DSC results reveal that combi-2 has a stabilizing effect on E. coli at any concentration while Pep-1 stabilizes the E. coli membrane only at high concentration. Both peptides show a preferential interaction with one of the anionic lipids leading to clustering in E. coli membrane. SEM images reveal that Pep-1 and combi-2 form superstructures including fibrils in the presence of E. coli membrane mimicking vesicles. Calorimetric and spectroscopic techniques may be used in a complementary way with imaging techniques to gain more insights into peptide-lipid interactions.

Direct detection of residual cyanide in cassava using spectroscopic techniques

Fluorescence, infrared, scanning electron microscopy (SEM), UV-visible, and X-ray diffraction (XRD) techniques have been applied to monitor the effect of processing mode on the residual cyanogens in cassava roots. The processed samples' infrared spectra have shown that only the boiled sample contains residual cyanide. SEM micrographs have revealed that irregularly shaped granules of about 100-microm size contain cyanide, while spherical granules of about 10-microm size do not. X-ray diffraction patterns have shown that the intensities of peaks are not affected by the presence of cyanide in the cassava samples. Fluorescence and UV-visible studies have detected the presence of cyanide converted to cyanate in water used for soaking processes. The thermal behavior of cassava samples with respect to the cyanide content and the role of oxygen and different ions present in water used for soaking processes are also discussed.

A vibrational study of the nature of hydroxyl groups chemical bonding in two aluminium hydroxides

Lengths, strengths and valences of OH bonds in the two aluminium hydroxides gibbsite and bayerite were determined on the basis of vibrational spectral data. The uncoupled OD stretching modes in the range 2400-2800cm(-1) were recorded by means of infrared diffuse reflectance, thereby avoiding effects of surface, vibrational coupling or particle shape. The assignment of the corresponding Raman spectra resulted in the determination of harmonic wavenumbers, force constants and anharmonicity coefficients of bulk OH groups in the two minerals. OH bond lengths deduced from these data varied from 0.964A to 0.975A in gibbsite and 0.962A to 0.973A in bayerite. These lengths appear to correspond to weak H-bonds contrary to previously recognized data from X-ray diffraction and neutron diffraction studies. Finally, bond valences were calculated on the basis of these new bond lengths and discussed as a function of crystallographic structures and the nature of hydrogen bonding in these two structures.

Proline-Modified (RW)n Peptides: Enhancing the Antimicrobial Efficacy and Selectivity against Multidrug-Resistant Pathogens

The growing threat of multidrug-resistant (MDR) bacteria necessitates the development of novel antimicrobial agents. This study investigates the potential of proline-modified (RW)n peptides as a platform for combating MDR pathogens with minimal toxicity. We synthesized and evaluated (RW)n peptides (n = 4, 6, and 8) with and without central proline residues against five clinically relevant bacterial strains, including ESKAPE pathogens. Antimicrobial activity, cytotoxicity, and synergistic effects with conventional antibiotics were assessed. Proline incorporation significantly enhanced the peptide selectivity and broadened the spectrum of activity, particularly against Gram-negative bacteria. RW6P and RW8P demonstrated exceptional efficacy (MICs ≤ 0.25 μg/mL) against methicillin-resistant Staphylococcus aureus and Escherichia coli with minimal toxicity to human cells. Notably, RW8P restored ampicillin susceptibility in Pseudomonas aeruginosa (MIC < 0.25 μg/mL) without dose-dependent toxicity. Exceptionally, RW6-2P demonstrated efficacy against all Gram-positive and Gram-negative bacteria, except Klebsiella pneumoniae (Kp), without toxicity. Furthermore, several Gram-negative isolates were rendered susceptible to vancomycin when combined with these peptides, addressing a key limitation of glycopeptide antibiotics. Gram-negative Klebsiella pneumoniae (Kp) was rendered susceptible to vancomycin when combined with RW4P and RW6-2P. RW4P and RW6-2P, with and without antibiotics, have shown selectivity. This study presents proline-modified (RW)n peptides as promising candidates for developing broad-spectrum antimicrobials with enhanced selectivity and the potential to revitalize existing antibiotics against MDR pathogens.

Proline-Modified RWn Peptides: Enhanced Antifungal Efficacy and Synergy with Conventional Antibiotics for Combating Resistant Fungal Infections

Candida albicans (Ca) and Cryptococcus neoformans (Cn) infections pose a growing threat due to rising antifungal resistance. This study explores a new class of antifungal agents, the RWn series (n = 4, 6, 8) peptides. These synthetic peptides were evaluated for their ability to inhibit Ca and Cn growth. All peptides except RW4 displayed antifungal activity, with RW6 exhibiting exceptional potency against Cn. Importantly, the incorporation of a proline residue significantly reduced cytotoxicity while maintaining antifungal activity against Cn for all RWnP peptides. Notably, RW6P demonstrated broad-spectrum activity against both Ca and Cn with low minimum inhibitory concentrations (MICs) and minimal toxicity. Furthermore, combining RW6P with trace amounts of traditional antibiotics (penicillin, vancomycin, and ampicillin) achieved synergistic effects, significantly reducing MICs against both fungi. These findings suggest that RWnP peptides, particularly RW6P, have promising potential as novel antifungal agents due to their high potency, broad-spectrum activity, and ability to resensitize fungi to existing antibiotics.