Vijayalekshmi Sarojini

Antimicrobial peptides with potential for biofilm eradication: synthesis and structure activity relationship studies of battacin peptides.

We report on the first chemical syntheses and structure-activity analyses of the cyclic lipopeptide battacin which revealed that conjugation of a shorter fatty acid, 4-methyl-hexanoic acid, and linearization of the peptide sequence improves antibacterial activity and reduces hemolysis of mouse blood cells. This surprising finding of higher potency in linear lipopeptides than their cyclic counterparts is economically beneficial. This novel lipopeptide was membrane lytic and exhibited antibiofilm activity against Pseudomonas aeruginosa, Staphylococcus aureus, and, for the first time, Pseudomonas syringe pv. actinidiae. The peptide was unstructured in aqueous buffer and dimyristoylphosphatidylcholine-polymerized diacetylene vesicles, with 12% helicity induced in 50% v/v of trifluoroethanol. Our results indicate that a well-defined secondary structure is not essential for the observed antibacterial activity of this novel lipopeptide. A truncated pentapeptide conjugated to 4-methyl hexanoic acid, having similar potency against Gram negative and Gram positive pathogens was identified through alanine scanning.

Recent developments in anticancer drug delivery using cell penetrating and tumor targeting peptides

ABSTRACT Efficient intracellular trafficking and targeted delivery to the site of action are essential to overcome the current drawbacks of cancer therapeutics. Cell Penetrating Peptides (CPPs) offer the possibility of efficient intracellular trafficking, and, therefore the development of drug delivery systems using CPPs as cargo carriers is an attractive strategy to address the current drawbacks of cancer therapeutics. Additionally, the possibility of incorporating Tumor Targeting Peptides (TTPs) into the delivery system provides the necessary drug targeting effect. Therefore the conjugation of CPPs and/or TTPs with therapeutics provides a potentially efficient method of improving intracellular drug delivery mechanisms. Peptides used as cargo carriers in DDS have been shown to enhance the cellular uptake of drugs and thereby provide an efficient therapeutic benefit over the drug on its own. After providing a brief overview of various drug targeting approaches, this review focusses on peptides as carriers and targeting moieties in drug‐peptide covalent conjugates and summarizes the most recent literature examples where CPPs on their own or CPPs together with TTPs have been conjugated to anticancer drugs such as Doxorubicin, Methotrexate, Paclitaxel, Chlorambucil etc. A short section on CPPs used in multicomponent drug delivery systems is also included.

An antibacterial pyrazole derivative from Burkholderia glumae, a bacterial pathogen of rice

Burkholderia glumae, a bacterial pathogen on rice, produced compounds in liquid culture that, in agar diffusion assays, gave strong inhibitory action against Erwinia amylovora, the bacterium responsible for fire blight disease of apple and pear trees. Products were isolated from culture medium by cation exchange and then purified by bioassay-guided chromatographic methods. Two major products were obtained, one of which was not active when fully purified. Each product showed a single ninhydrin-staining spot on TLC and a single HPLC peak. The non-active product was deduced from NMR, MS, and chemical data, to be the tripeptide L-alanyl-L-homoserinyl-L-aspartate. The NMR data for the active product demonstrated that it contained the same tripeptide, but functionalised at the beta-carboxyl of the C-terminal aspartate, by a moiety that provided an additional 98 mass units to the parent tripeptide. Various data led to the interpretation that this moiety was a highly unusual oxygenated pyrazole structure, and thus the bioactive product was deduced to be 3-[L-alanyl-L-homoserinyl-L-aspartyl-beta-carboxy]-4-hydroxy-5-oxopyrazole. This compound was found to inhibit the growth of a number of different bacterial species.

Feasibility Study Exploring the Potential of Novel Battacin Lipopeptides as Antimicrobial Coatings

Colonization of medical implant surfaces by pathogenic microorganisms causes implant failure and undermines their clinical applicability. Alarming increase in multidrug-resistant bacteria poses serious concerns with the use of medical implants. Antimicrobial peptides (AMPs) that form part of the innate immune system in all forms of life are attractive alternatives to conventional antibiotics to treat multidrug-resistant bacterial biofilms. The aim of this study was to assess the in vitro antibacterial potency of our recently discovered lipopeptides from the battacin family upon immobilization to various surfaces. To achieve this, glass, silicon, and titanium surfaces were functionalized through silanization followed by addition of the heterobifunctional cross-linker, succinimidyl-[N-maleimidopropionamido]-poly(ethylene glycol) ester to generate maleimide-functionalized surfaces. The lipopeptide, GZ3.27, with an added N-terminal cysteine was covalently coupled to the surfaces via a thioether bond through a Michael-type addition between the cysteine sulfhydryl group and the maleimide moiety. Success of surface immobilization and antimicrobial activity of the coated surfaces was assessed using water contact angle measurements, X-ray photoelectron spectroscopy, ellipsometry, scanning electron microscopy, colony forming unit assays and biofilm analysis. The lipopeptide-coated surfaces caused significant damage to the cellular envelop of Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli) upon contact and prevented surface colonization by P. aeruginosa and E. coli biofilms. The lipopeptides investigated in this study were not hemolytic to mouse blood cells in solution. Findings from this study indicate that these lipopeptides have the potential to be developed as promising antimicrobial coatings on medical implants.

Antimicrobial peptides against Pseudomonas syringae pv. actinidiae and Erwinia amylovora: Chemical synthesis, secondary structure, efficacy, and mechanistic investigations.

We report on structurally modified dodecapeptide amides (KYKLFKKILKFL‐NH2) and two analogs of a hexapeptide amide (WRWYCR‐NH2) with antibacterial activity against the Gram negative pathogens Pseudomonas syringae pv. actinidiae (Psa) and Erwinia amylovora (Ea). Dodecapeptide minimal inhibitory concentrations (MICs) ranged from 3.2 to 15.4 µM, with the unmodified peptide being the most potent against both pathogens. The unmodified dodecapeptide also had 32–58% α‐helicity in membrane mimetic environments (50% v/v trifluoroethanol and 30 mM SDS micelles). Structural modifications which included branching, acylation, and conjugation with 5‐nitro‐2‐furaldehyde (NFA) proved detrimental to both antimicrobial activity and α‐helicity. Scanning electron microscopy (SEM) revealed distinct morphological changes to bacterial cells treated with the different peptides, leading to blistering of the membrane and cell lysis. MICs of the hexapeptide amide were 3.9–7.7 µM against both pathogens. The hexapeptide acid did not show anti‐bacterial activity against either pathogen. However, the NFA conjugated hexapeptide acid was more active than the parent peptide or NFA alone with MICs of 1.6–3.2 µM against the pathogens. SEM analysis revealed shriveling and collapse of bacterial cells treated with the hexapeptide, whereas shortening and compactness on exposure to streptomycin. A colorimetric assay demonstrated that the dodecapeptides were likely to act by targeting the bacterial membrane, whereas the hexapeptides, streptomycin, and NFA were not, thereby supporting the morphological changes observed during SEM. To the best of our knowledge, this appears to be the first report of antimicrobial peptide activity against Psa, a pathogen that is currently devastating the kiwifruit industry internationally.

Preptin Analogues: Chemical Synthesis, Secondary Structure and Biological Studies

Peptide hormones that modulate insulin secretion have been recognized to have therapeutic potential, with peptides such as amylin (pramlintide acetate, Symlin) and exendin‐4 (exenatide, Byetta) now commercially available. Preptin is a peptide that has been shown to increase insulin secretion in vitro and in vivo. Here, we describe the first chemical synthesis and analysis of a short series of preptin analogues based on the rat preptin sequence. Phe 21 in the preptin sequence was substituted with the non‐protein amino acids D‐Phe, D‐Hphe, 3‐aminobenzoic acid and 1‐aminocyclooctane‐1‐carboxylic acid, which rendered the preptin analogues resistant to chymotryptic protease hydrolysis at this position. Substitution of Phe 21 with these non‐protein amino acids did not abrogate the insulin secretory effect of preptin, with analogues showing a similar dose‐dependent effect on insulin secretion from βTC6‐F7 mouse β‐cells in both the presence and absence of glucose as unmodified rat preptin. Further studies on the stability of the preptin analogues and their effect on insulin secretion are in progress.

Recent Developments in Antimicrobial-Peptide-Conjugated Gold Nanoparticles

The escalation of multidrug-resistant pathogens has created a dire need to develop novel ways of addressing this global therapeutic challenge. Because of their antimicrobial activities, the combination of antimicrobial peptides (AMPs) and nanoparticles is a promising tool with which to kill drug-resistant pathogens. In recent years, several studies using AMP-nanoparticle conjugates, especially metallic nanoparticles, as potential antimicrobial agents against drug-resistant pathogens have been published. Among these, antimicrobial-peptide-conjugated gold nanoparticles (AMP-AuNPs) are particularly attractive because of the nontoxic nature of gold and the possibility of fine-tuning the AMP-NP conjugation chemistry. The following review discusses recent developments in the synthesis and antimicrobial activity studies of AMP-AuNPs. The classification of AMPs, their mechanisms of action, methods used for functionalizing AuNPs with AMPs, and the antimicrobial activities of the conjugates are discussed.

Effect of Antifreeze Peptide Pretreatment on Ice Crystal Size, Drip Loss, Texture, and Volatile Compounds of Frozen Carrots

Ice crystal formation is of primary concern to the frozen food industry. In this study, the effects of antifreeze peptides (AFPs) on ice crystal formation were assessed in carrot during freezing and thawing. Three synthetic analogues based on naturally occurring antifreeze peptides were used in this study. The AFPs exhibited modification of ice crystal morphology, confirming their antifreeze activity in vitro. The ability of the synthetic AFPs to minimize drip loss and preserve color, structure, texture, and volatiles of frozen carrot was evaluated using the techniques of SEM, GC-MS, and texture analysis. The results prove the potential of these AFPs to preserve the above characteristics in frozen carrot samples.

Synthesis and cytotoxicity of thieno[2,3-b]quinoline-2-carboxamide and cycloalkyl[b]thieno[3,2-e]pyridine-2-carboxamide derivatives.

Seventy nine derivatives of thieno[2,3-b]quinolines, tetrahydrothieno[2,3-b]quinoline, dihydrocyclopenta[b]thieno[3,2-e]pyridine, cyclohepta[b]thieno[3,2-e]pyridine and hexahydrocycloocta[b]thieno[3,2-e]pyridine were either synthesized or obtained commercially and tested for their antiproliferative activity against HCT116, MDA-MB-468 and MDA-MB-231 human cancer cell lines. The most potent eight compounds were active against all cell lines with IC50 values in the 80-250nM range. In general hexahydrocycloocta[b]thieno[3,2-e]pyridines were most active with increasing activity observed as larger cycloalkyl rings were fused to the pyridine ring.

Intrinsically unstructured proteins by design—electrostatic interactions can control binding, folding, and function of a helix‐loop‐helix heterodimer

Intrinsically disordered proteins that exist as unordered monomeric structures in aqueous solution at pH 7 but fold into four‐helix bundles upon binding to recognized polypeptide targets have been designed. NMR and CD spectra of the monomeric polypeptides show the hallmarks of unordered structures, whereas in the bound state they are highly helical. Analytical ultracentrifugation data shows that the polypeptides bind to their targets to form exclusively heterodimers at neutral pH. To demonstrate the relationship between binding, folding, and function, a catalytic site for ester hydrolysis was introduced into an unordered and largely inactive monomer, but that was structured and catalytically active in the presence of a specific polypeptide target. Electrostatic interactions between surface‐exposed residues inhibited the binding and folding of the monomers at pH 7. Charge–charge repulsion between ionizable amino acids was thus found to be sufficient to disrupt binding between polypeptide chains despite their inherent propensities for structure formation and may be involved in the folding and function of inherently disordered proteins in biology. Copyright