Design of a cyclic peptide targeting intracellular Staphylococcus aureus

Area of Science:

• Biochemistry
• Molecular Biology
• Drug Discovery

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant clinical challenge, especially intracellular infections, due to difficulties in antimicrobial drug delivery.
• Existing antimicrobial agents struggle to achieve the necessary stability, host-cell penetration, and bacterial target engagement for intracellular pathogens.

Purpose of the Study:

• To engineer a novel cyclic peptide, MCo-KTR2, by grafting an antimicrobial peptide (KTR) onto a cyclotide scaffold (MCoTI-I).
• To evaluate MCo-KTR2's potential as an intracellular antimicrobial agent against MRSA, focusing on stability, cellular uptake, and efficacy.

Main Methods:

• Molecular docking and dynamics simulations to predict interactions with MRSA's penicillin-binding protein PBP2a.
• Site-directed mutagenesis and fluorescence polarization assays to identify key binding residues.
• In vitro assays to assess serum stability, cellular uptake, intracellular activity, cytotoxicity, and haemolytic activity.
• Combination studies with other antimicrobial agents (Visomitin, vancomycin, gentamicin).

Main Results:

• MCo-KTR2 demonstrated a >30-fold increase in serum stability and enhanced cellular uptake compared to linear KTR.
• The engineered peptide colocalized with intracellular MRSA and showed improved activity against intracellular bacteria.
• MCo-KTR2 exhibited no detectable cytotoxicity or haemolytic activity.
• Combination therapies enhanced MCo-KTR2's antibacterial efficacy.

Conclusions:

• Cyclotide grafting is an effective strategy for enhancing peptide stability and intracellular delivery of antimicrobial agents.
• MCo-KTR2 shows promise as a scaffold for developing novel therapeutics against intracellular MRSA infections.
• Further optimization of MCo-KTR2 could lead to improved treatments for challenging bacterial infections.