Here we used a new strategy for exploring the peptide chemical space to discover bicyclic antimicrobial peptides.

We used the concept of chemical space to explore a virtual library of bicyclic peptides formed by double thioether cyclization of a precursor linear peptide, and identified an antimicrobial bicyclic peptide (AMBP) with remarkable activity against several MDR strains of Acinetobacter baumannii and Pseudomonas aeruginosa.

The peptide α-helix is right-handed when containing amino acids with L-chirality, and left-handed with D-chirality, however mixed chirality peptides generally do not form α-helices unless the non-natural residue amino-isobutyric acid...

A new family of cyclic antimicrobial peptides is reported targeting multidrug resistant Pseudomonas aeruginosa by membrane disruption.

AimIn the present work, the potential of the D-enantiomeric dendrimers dG3KL and dTNS18 was evaluated in relation to tobramycin (Tob), for the development of novel antibacterials to treat Pseudomonas aeruginosa chronic lung infections in patients with cystic fibrosis.ResultsThe activity of dendrimers against planktonic P. aeruginosa cells was less than Tob against three of the four strains tested (median minimum inhibitory concentration [MIC] 8 vs 1 µg/mL, respectively), but 32-fold higher against the PaPh32 strain isolated at posttransplantation stage. Results from comparative minimum bactericidal concentration/MIC evaluation and time–kill assay suggested a bactericidal mechanism for all test agents. Subinhibitory concentrations of both dendrimers and Tob significantly affected biofilm formation by all strains in a dose-dependent manner, although the PaPh26 strain, isolated during the chronic stage of infection, was particularly susceptible to dendrimers. The activity of dendrimers against preformed P. aeruginosa biofilm was generally comparable to Tob, considering both dispersion and viability of biofilm. Particularly, exposure to the test agent at 10 × MIC caused significant biofilm death (>90%, even to eradication), though with strain-specific differences. Single administration of dendrimers or Tob at 10 × MIC was not toxic in Galleria mellonella wax-moth larvae over 96 hours. However, contrarily to Tob, dendrimers were not protective against systemic infection caused by P. aeruginosa in G. mellonella. Kinetics of P. aeruginosa growth in hemolymph showed that bacterial load increased over time in the presence of dendrimers.ConclusionOverall, our findings indicated that dG3KL and dTNS18 peptide dendrimers show in vitro activity comparable to Tob against both P. aeruginosa planktonic and biofilm cells at concentrations not toxic in vivo. Further studies are warranted to explore different dosages and to increase the bioavailability of the peptides to solve the lack of protective effect observed in G. mellonella larvae.

<p>The peptide α-helix is right-handed when containing amino acids with L-chirality, and left-handed with D-chirality. What happens in between is largely unknown, however α-helices have not been reported with mixed chirality sequences unless a strong non-natural helix inducer such as amino-isobutyric acid was used. Herein we report the discovery of a membrane disruptive amphiphilic antimicrobial undecapeptide containing seven L- and four D-residues forming a stable right-handed α-helix in stapled bicyclic and linear forms. The α-helical fold is evidenced by X-ray crystallography and supported in solution by circular dichroism spectra as well as molecular dynamics simulations. The linear mixed chirality peptide is as active as the L-sequence against multidrug resistant bacteria but shows no hemolysis and full stability against serum proteolysis. Searching for mixed chirality analogs preserving folding might be generally useful to optimize α-helical bioactive peptides. </p>

<p>The peptide α-helix is right-handed when containing amino acids with L-chirality, and left-handed with D-chirality. What happens in between is largely unknown, however α-helices have not been reported with mixed chirality sequences unless a strong non-natural helix inducer such as amino-isobutyric acid was used. Herein we report the discovery of a membrane disruptive amphiphilic antimicrobial undecapeptide containing seven L- and four D-residues forming a stable right-handed α-helix in stapled bicyclic and linear forms. The α-helical fold is evidenced by X-ray crystallography and supported in solution by circular dichroism spectra as well as molecular dynamics simulations. The linear mixed chirality peptide is as active as the L-sequence against multidrug resistant bacteria but shows no hemolysis and full stability against serum proteolysis. Searching for mixed chirality analogs preserving folding might be generally useful to optimize α-helical bioactive peptides. </p>

<p></p><p>The peptide α-helix is right-handed when containing amino acids with L-chirality, and left-handed with D-chirality, however mixed chirality peptides generally do not form α-helices unless the non-natural residue amino-isobutyric acid is used as helix inducer. Herein we report the first X-ray crystal structures of mixed chirality α-helices in short peptides comprising only natural residues at the example of a stapled bicyclic and a linear membrane disruptive amphiphilic antimicrobial peptide (AMP) containing seven L- and four D-residues, as complexes of fucosylated analogs with the bacterial lectin LecB. The mixed chirality α-helices are superimposable to their parent homochiral α-helices and form under similar conditions as shown by CD spectra and MD simulations but are resistant to proteolysis. The observation of mixed chirality α-helix with only natural residues in the protein environment of LecB suggests a vast unexplored territory of α-helical mixed chirality sequences and their possible use for optimizing bioactive α-helical peptides.</p><br><p></p>