Investigation of α/γ hybrid peptide self‐assembled structures with antimicrobial and antibiofilm properties

The present work describes the synthesis and characterization of α/γ hybrid peptides, Boc‐Phe‐γ⁴‐Phe‐Val‐OMe, P1 ; Boc‐Ala‐γ⁴‐Phe‐Val‐OMe, P2 ; and Boc‐Leu‐γ⁴‐Phe‐Val‐OMe, P3 together with the formation of self‐assembled structures formed by these hybrid peptides in dimethyl sulfoxide (DMSO)/water (1:1). The self‐assembled structures were characterized by infrared (IR) spectroscopy, circular dichroism (CD), and scanning electron microscopy (SEM). Further, α/γ hybrid peptide self‐assembled structures were evaluated for antibacterial properties. Among all, the self‐assembled peptide P1 exhibited the antimicrobial activity against Escherichia coli and Klebsiella pneumoniae, while self‐assembled peptide P3 inhibited the biofilms of Salmonella typhimurium and Pseudomonas aeruginosa. In this study, we have shown the significance of self‐assembled structures formed from completely hydrophobic α/γ hybrid peptides in exploring the antibacterial properties together with biofilm inhibition.     

Vanadate-resistant mutants of Candida albicans show alterations in phosphate uptake

Phosphate uptake studies in different strains of the dimorphic pathogenic yeast Candida albicans were undertaken to show that this yeast actively transported phosphate with an apparent Km in the range of 90-170 microM. The uptake was pH dependent and derepressible under phosphate starvation. Vanadate-resistant (van) mutants of C. albicans showed a 20-70% reduction in the rate of phosphate uptake in high phosphate medium and was associated with an increased Km and reduced Vmax. The magnitude of derepression under phosphate starvation was different between van mutants. These results demonstrate that van mutants may have developed resistance by modifying the rate of entry of vanadate.     

Ribbon structure stabilized by C10 and C12 turns in αγ hybrid peptide

The present study describes the synthesis and crystallographic analysis of αγ hybrid peptides, Boc‐Gpn‐L‐Pro‐NHMe ( 1 ), Boc‐Aib‐Gpn‐L‐Pro‐NHMe ( 2 ), and Boc‐L‐Pro‐Aib‐Gpn‐L‐Pro‐NHMe ( 3 ). Peptides 1 and 2 adopt expanded 12‐membered (C₁₂) helical turn over γα segment. Peptide 3 promotes the ribbon structure stabilized by type II β‐turn (C₁₀) followed by the expanded C₁₂ helical γα turn. Both right‐handed and left‐handed helical conformations for Aib residue are observed in peptides 2 and 3 , respectively Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

Tuning the beta-turn segment in designed peptide beta-hairpins: construction of a stable type I' beta-turn nucleus and hairpin-helix transition promoting segments

Designed octapeptides Boc-Leu-Val-Val-Aib-(D)Xxx-Leu-Val-Val-OMe ((D)Xxx = (D)Ala, 3a;(D)Val, 3c and (D)Pro, 5a) and Boc-Leu-Phe-Val-Aib-(D)Ala-Leu-Phe-Val-OMe (3b) have been investigated to construct models of a stable type I' beta-turn nucleated hairpin and to generate systems for investigating helix-hairpin conformational transitions. Peptide 5a, which contains a central Aib-(D)Pro segment, is shown to adopt a stable type I' beta-turn nucleated hairpin structure, stabilized by four cross-strand hydrogen bonds. The stability of the structure in diverse solvents is established by the observation of all diagnostic NOEs expected in a beta-hairpin conformation. Replacement of (D)Pro5 by (D)Ala/(D)Val (3a-c) results in sequences that form beta-hairpins in hydrogen bonding solvents like CD(3)OH and DMSO-d(6). However, in CDCl(3) evidence for population of helical conformations is obtained. Peptide 6b (Boc-Leu-Phe-Val-Aib-Aib-Leu-Phe-Val-OMe), which contains a centrally positioned Aib-Aib segment, provides a clear example of a system, which exhibits a helical conformation in CDCl(3) and a significant population of both helices and hairpins in CD(3)OH and DMSO-d(6). The coexistence of multiple conformations is established by the simultaneous observation of diagnostic NOEs. Control over stereochemistry of the central beta-turn permits generation of models for robust beta-hairpins and also for the construction of systems that may be used to probe helix-hairpin conformational transitions.     

Synthesis of amides from (E)-3-(1-chloro-3,4-dihydronaphthalen-2-yl)acrylic acid and substituted amino acid esters as NorA efflux pump inhibitors of Staphylococcus aureus

Inhibitors for NorA efflux pump of Staphylococcus aureus have attracted the attention of many researchers towards the discovery and development of novel efflux pump inhibitors (EPIs). In an attempt to find specific potent inhibitors of NorA efflux pump of S. aureus, a total of 15 amino acid conjugates of 3-(1-chloro-3,4-dihydronaphthalen-2-yl)acrylic acid (4–18) were synthesized using a simple convenient synthetic approach and bioevaluated against NorA efflux pump. Two compounds 7 and 8 (each having MEC of 1.56?µg/mL) were found to restore the activity of ciprofloxacin through reduction of the MIC elucidated by comparing the ethidium bromide efflux in dose dependent manner in addition to ethidium bromide efflux inhibition and accumulation study using NorA overexpressing strain SA-1199B. Most potent compounds among these were able to restore the antibacterial activity of ciprofloxacin completely against SA-1199B. Structure activity relationship (SAR) studies and docking study of potent compounds 7 and 8 could elucidate the structural requirements necessary for interaction with the NorA efflux pumps. On the whole, compounds 7 and 8 have ability to reverse the NorA efflux mediated resistance and could be further optimized for development of potent efflux pump inhibitors.     

Conformations of beta-amino acid residues in peptides: X-ray diffraction studies of peptides containing the achiral residue 1-aminocyclohexaneacetic acid, beta3,3Ac6c

The conformational preferences of the 3,3-disubstituted beta-amino acid residue, 1-aminocyclohexaneacetic acid (beta3,3Ac6c) have been investigated by determining the crystal structures of the parent amino acid, the hydrochloride derivative, 10 protected derivatives and di and tripeptides. The symmetrical cyclohexyl substituent at the beta-position restricts the values of the torsion angles phi (N--C(beta)) and theta (C(beta)--C(alpha)) to approximately gauche values (+/-60 degrees ). Relatively few intramolecularly hydrogen bonded conformations are observed. In the dipeptide Boc-beta(3,3)Ac6c-beta(3,3)Ac6c-NHMe a C6 hydrogen bond is observed. In Piv-Pro-beta(3,3)Ac6c-NHMe a C11 hydrogen bonded hybrid alphabeta turn is characterized. In a majority of cases the amino group occupies the axial position in the cyclohexane ring. The conformations observed are compared with crystallographically observed structures for other beta-residues, including beta(2,2)Ac6c.     

Conformation of di-n-propylglycine residues (Dpg) in peptides: crystal structures of a type I' beta-turn forming tetrapeptide and an alpha-helical tetradecapeptide.

The crystal structures of two oligopeptides containing di-n-propylglycine (Dpg) residues, Boc-Gly-Dpg-Gly-Leu-OMe (1) and Boc-Val-Ala-Leu-Dpg-Val-Ala-Leu-Val-Ala-Leu-Dpg-Val-Ala-Leu-OMe (2) are presented. Peptide 1 adopts a type I'beta-turn conformation with Dpg(2)-Gly(3) at the corner positions. The 14-residue peptide 2 crystallizes with two molecules in the asymmetric unit, both of which adopt alpha-helical conformations stabilized by 11 successive 5 --> 1 hydrogen bonds. In addition, a single 4 --> 1 hydrogen bond is also observed at the N-terminus. All five Dpg residues adopt backbone torsion angles (phi, psi) in the helical region of conformational space. Evaluation of the available structural data on Dpg peptides confirm the correlation between backbone bond angle N-C(alpha)-C' (tau) and the observed backbone phi,psi values. For tau > 106 degrees, helices are observed, while fully extended structures are characterized by tau < 106 degrees. The mean tau values for extended and folded conformations for the Dpg residue are 103.6 degrees +/- 1.7 degrees and 109.9 degrees +/- 2.6 degrees, respectively.     

Synthesis,characterization, and wound healing properties of α/γ hybrid peptides

The present work describes the synthesis, characterization, and wound healing properties of α/γ hybrid peptides: Boc-Phe-γ⁴-Phe-Val-OMe ( S1 ), Boc-^DPhe-γ⁴-Phe-Val-OMe ( S2 ), Boc-Ala-γ⁴-Phe-Val-OMe ( S3 ), Boc-^DAla-γ⁴-Phe-Val-OMe ( S4 ), Boc-Leu-γ⁴-Phe-Val-OMe ( S5 ), and Boc-^DLeu-γ⁴-Phe-Val-OMe ( S6 ). Peptides S1–S6 were screened against human keratinocytes (HaCaT) and RAW 264.7 cells. Among all, S1 - and S2 -treated cells exhibited high cell viability; S1 and S2 induced keratinocyte migration and inhibited the production of the cytokines IL-6 and TNF-α. In vivo results demonstrated that the hybrid peptides S1 and S2 accelerate wound healing in Wistar rats with 83% and 88% at 50 μg/ml, and 74% and 76% at 25 μg/ml, respectively.