Presenting Antimicrobial Peptides on Poly(ethylene glycol): Star-Shaped vs Comb-Like Architectures

Abstract

Conjugating antimicrobial peptides (AMPs) to nonlinear polymers is a promising strategy to overcome the translational challenges of AMPs toward treating infections caused by antibiotic-resistant bacteria. Nonlinear polymers, and therefore conjugates, can be prepared with various architectures (e.g., star-shaped, comb-like, hyperbranched, etc.), however, the effects of polymer architecture on antimicrobial performance and related properties, like size and morphology in solution and secondary structure, are not yet well-understood. Here, we compare conjugates of the human chemokine-derived AMP stapled P9 with poly(ethylene glycol) (PEG) prepared in two of the major nonlinear architectures: star-shaped and comb-like. At comparable molecular weights and compositions (peptide wt %), comb-like conjugates afford increased helicity, solubility, antimicrobial activity, and proteolytic stability compared to star-shaped analogs. We then leveraged the expansive design space of comb-like architectures to prepare conjugates with different backbone lengths and PEG side chain lengths, with shorter PEG side chains leading to increased helicity, yet potentially less shielding from proteolytic degradation and the longest backbone lengths furnishing the most potent antimicrobial activity. Both comb-like and star-shaped conjugates display high zeta potential, indicating that the cationic AMPs were accessible for electrostatic interactions with bacterial membranes. Yet, the comb-like conjugates showed a higher fraction of unimolecular structures indicative of a lower propensity for supramolecular assembly that could be encumbering the desired AMP-bacteria interactions in the star-shaped conjugates. Together, our work shows comb-like AMP-polymer conjugates to outperform analogous star-shaped conjugates, while adding design flexibility to access an expansive range of monomer chemistries, monomer distributions, and backbone lengths to modulate performance-determining properties and ultimately furnish an effective suite of AMP-polymer materials as alternatives to conventional antibiotics for combatting bacterial infections.