Effect of distal sugar and interglycosidic linkage of disaccharides on the activity of proline rich antimicrobial glycopeptides

Inhibition of translation termination by the antimicrobial peptide Drosocin

The proline-rich antimicrobial peptide (PrAMP) Drosocin (Dro) from fruit flies shows sequence similarity to other PrAMPs that bind to the ribosome and inhibit protein synthesis by varying mechanisms. The target and mechanism of action of Dro, however, remain unknown. Here we show that Dro arrests ribosomes at stop codons, probably sequestering class 1 release factors associated with the ribosome. This mode of action is comparable to that of apidaecin (Api) from honeybees, making Dro the second member of the type II PrAMP class. Nonetheless, analysis of a comprehensive library of endogenously expressed Dro mutants shows that the interactions of Dro and Api with the target are markedly distinct. While only a few C-terminal amino acids of Api are critical for binding, the interaction of Dro with the ribosome relies on multiple amino acid residues distributed throughout the PrAMP. Single-residue substitutions can substantially enhance the on-target activity of Dro.

Structural basis for translation inhibition by the glycosylated drosocin peptide

The proline-rich antimicrobial peptide (PrAMP) drosocin is produced by Drosophila species to combat bacterial infection. Unlike many PrAMPs, drosocin is O-glycosylated at threonine 11, a post-translation modification that enhances its antimicrobial activity. Here we demonstrate that the O-glycosylation not only influences cellular uptake of the peptide but also interacts with its intracellular target, the ribosome. Cryogenic electron microscopy structures of glycosylated drosocin on the ribosome at 2.0-2.8-Å resolution reveal that the peptide interferes with translation termination by binding within the polypeptide exit tunnel and trapping RF1 on the ribosome, reminiscent of that reported for the PrAMP apidaecin. The glycosylation of drosocin enables multiple interactions with U2609 of the 23S rRNA, leading to conformational changes that break the canonical base pair with A752. Collectively, our study reveals novel molecular insights into the interaction of O-glycosylated drosocin with the ribosome, which provide a structural basis for future development of this class of antimicrobials.

Glycosylation and Lipidation Strategies: Approaches for Improving Antimicrobial Peptide Efficacy

Antimicrobial peptides (AMPs) have recently gained attention as a viable solution for combatting antibiotic resistance due to their numerous advantages, including their broad-spectrum activity, low propensity for inducing resistance, and low cytotoxicity. Unfortunately, their clinical application is limited due to their short half-life and susceptibility to proteolytic cleavage by serum proteases. Indeed, several chemical strategies, such as peptide cyclization, N-methylation, PEGylation, glycosylation, and lipidation, are widely used for overcoming these issues. This review describes how lipidation and glycosylation are commonly used to increase AMPs’ efficacy and engineer novel AMP-based delivery systems. The glycosylation of AMPs, which involves the conjugation of sugar moieties such as glucose and N-acetyl galactosamine, modulates their pharmacokinetic and pharmacodynamic properties, improves their antimicrobial activity, and reduces their interaction with mammalian cells, thereby increasing selectivity toward bacterial membranes. In the same way, lipidation of AMPs, which involves the covalent addition of fatty acids, has a significant impact on their therapeutic index by influencing their physicochemical properties and interaction with bacterial and mammalian membranes. This review highlights the possibility of using glycosylation and lipidation strategies to increase the efficacy and activity of conventional AMPs.

Chemically modified and conjugated antimicrobial peptides against superbugs

Antimicrobial resistance (AMR) is one of the greatest threats to human health that, by 2050, will lead to more deaths from bacterial infections than cancer. New antimicrobial agents, both broad-spectrum and selective, that do not induce AMR are urgently required. Antimicrobial peptides (AMPs) are a novel class of alternatives that possess potent activity against a wide range of Gram-negative and positive bacteria with little or no capacity to induce AMR. This has stimulated substantial chemical development of novel peptide-based antibiotics possessing improved therapeutic index. This review summarises recent synthetic efforts and their impact on analogue design as well as their various applications in AMP development. It includes modifications that have been reported to enhance antimicrobial activity including lipidation, glycosylation and multimerization through to the broad application of novel bio-orthogonal chemistry, as well as perspectives on the direction of future research. The subject area is primarily the development of next-generation antimicrobial agents through selective, rational chemical modification of AMPs. The review further serves as a guide toward the most promising directions in this field to stimulate broad scientific attention, and will lead to new, effective and selective solutions for the several biomedical challenges to which antimicrobial peptidomimetics are being applied.

Comparing naturally occurring glycosylated forms of proline rich antibacterial peptide, Drosocin

Antimicrobial peptides (AMPs) are key players of innate immunity. Amongst various classes of AMPs, proline rich AMPs from insects enjoy special attention with few members of this class bearing O-glycosylation as post-translational modification. Drosocin, a 19 amino acid glycosylated AMP is a member of proline rich class, synthesized in the haemolymph of Drosophila melanogaster upon bacterial challenge. We report herein the chemical synthesis of drosocin carrying disaccharide (β-Gal(1 → 3)α-GalNAc) and comparison of its structural and functional properties with another naturally occurring monoglycosylated form of drosocin i.e. α-GalNAc-drosocin as well as with non-glycosylated drosocin. The disaccharide containing drosocin exhibited lower potency compared to monoglycosylated drosocin against all the tested Gram negative bacteria, suggesting the role of the distal sugar or increase in the sugar chain length on the activity. Circular dichroism studies failed to demonstrate the differential effect of sugars on the overall peptide conformation. Haemolytic and cytotoxic properties of drosocin were not altered due to an increase in the sugar chain length. In addition, we have also evaluated the effect of differentially glycosylated drosocins on two pro-inflammatory cytokines secreted by murine macrophages or LPS stimulated macrophages. All the drosocin forms tested, neither could stimulate the secretion of TNF-α and IL-6 nor could modulate LPS-induced levels of TNF-α and IL-6 in murine macrophages. This study provides insights about naturally occurring two different glycosylated forms of drosocin.