Polyoxometalate-polypeptide assemblies as peroxidase surrogates

Abstract

Developing artificial metalloenzymes that possess superior performance or properties than their natural counterparts is an attractive concept. Taking the simplest building blocks of naturally occurring enzymes, peptides and metal ions, scientists have developed systems that can compete with evolved proteins like peroxidases. Polyoxometalates (POMs) represent a class of anionic molecular metal-oxides with excellent redox properties. Recently, Wang’s group explored the peroxidase activity of different POMs, finding that some POMs displayed activity at basic pH. We have recently introduced a new type of hybrid material called “POMlymers”, which are covalently conjugated POM-peptide hybrids obtained through a ring-opening polymerization (ROP) reaction initiated by an amino group on the POM molecule. This is the first example of ROP of N-carboxyanhydrides (NCAs) using a molecular metal-oxide as initiator and inorganic molecular scaffold. POMlymer coatings showed antibacterial and antibiofilm activity. Attracted by the idea of preparing artificial metalloenzymes, we explored the self-assembly of these POMlymer hybrids in solution to identify a suitable environment for catalysis. In this communication, we present the preparation of supramolecular nanoscale assemblies based on a POMlymer with amphiphilic random copolypeptides that display peroxidase-like activity. We demonstrated that the covalent hybrid enhances the catalytic properties, compared to the free POM anion; whereas the ionic assembly has a detrimental effect on the catalysis. We also found that the catalytic activity of the covalent hybrid was enhanced in the assembled state. Finally, we evaluated the antimicrobial activity of POMK10 aggregates against Staphylococcus epidermidis and measured the bacteria response to this redoxactive hybrid material by measuring the production of biofilm and endogenous radical oxygen species (ROS). With this study we aimed at answering whether the POM-peptide covalent linkage could be advantageous to prepare hybrid materials that preserve the redox-active center. We used peroxidase activity and microbiology to address such a question.