Mixed Chirality α-Helix in a Stapled Bicyclic and a Linear Antimicrobial Peptide Revealed by X-Ray Crystallography

<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>

Mixed Chirality α-Helix in a Stapled Bicyclic and a Linear Antimicrobial Peptide Revealed by X-Ray Crystallography

<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>

Mixed Chirality α-Helix in a Stapled Bicyclic and a Linear Antimicrobial Peptide Revealed by X-Ray Crystallography

<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>

Mixed Chirality α-Helix in a Stapled Bicyclic and a Linear Antimicrobial Peptide Revealed by X-Ray Crystallography

<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>

Leucokinin mimetic elicits aversive behavior in mosquito Aedes aegypti (L.) and inhibits the sugar taste neuron

Insect kinins (leucokinins) are multifunctional peptides acting as neurohormones and neurotransmitters. In females of the mosquito vector Aedes aegypti (L.), aedeskinins are known to stimulate fluid secretion from the renal organs (Malpighian tubules) and hindgut contractions by activating a G protein-coupled kinin receptor designated “Aedae-KR.” We used protease-resistant kinin analogs 1728, 1729, and 1460 to evaluate their effects on sucrose perception and feeding behavior. In no-choice feeding bioassays (capillary feeder and plate assays), the analog 1728, which contains α-amino isobutyric acid, inhibited females from feeding on sucrose. It further induced quick fly-away or walk-away behavior following contact with the tarsi and the mouthparts. Electrophysiological recordings from single long labellar sensilla of the proboscis demonstrated that mixing the analog 1728 at 1 mM with sucrose almost completely inhibited the detection of sucrose. Aedae-KR was immunolocalized in contact chemosensory neurons in prothoracic tarsi and in sensory neurons and accessory cells of long labellar sensilla in the distal labellum. Silencing Aedae-KR by RNAi significantly reduced gene expression and eliminated the feeding-aversion behavior resulting from contact with the analog 1728, thus directly implicating the Aedae-KR in the aversion response. To our knowledge, this is the first report that kinin analogs modulate sucrose perception in any insect. The aversion to feeding elicited by analog 1728 suggests that synthetic molecules targeting the mosquito Aedae-KR in the labellum and tarsi should be investigated for the potential to discover novel feeding deterrents of mosquito vectors.

Study of ethylene kinetics during and after germination of sugar beet (Beta vulgarisL.) seeds and fruits

The interaction between ethylene production and seed germination of sugar beet (Beta vulgarisL.) was studied. For intact fruits, deoperculated fruits and true seeds, ethylene was only produced after the start of radicle emergence. Removal of the operculum or the whole pericarp, likely allowing better water uptake and gas exchange by the true seed, actually increased the time span between the start of radicle emergence and the beginning of ethylene production compared to intact fruits. ACC (1-aminocyclopropane-1-carboxylic acid), AOA (aminooxyacetic acid), AIB (2-amino isobutyric acid) and STS (silver thiosulphate) in the imbibition medium did not influence the germination pattern. Based on these findings, the function of ethylene during the germination of sugar beet is uncertain.