Photocatalytic degradation of bacterial lipopolysaccharides by peptide-coated TiO2 nanoparticles

In the present study, we investigated the degradation of both smooth and rough lipopolysaccharides from Gram-negative (LPS) and lipoteichoic acid from Gram-positive (LTA) bacteria by peptide-coated TiO2 nanoparticles (TiO2 NPs). While bare TiO2 NPs displayed minor binding to both LPS and LTA, coating TiO2 NPs with the antimicrobial peptide LL-37 dramatically increased binding to LPS and LTA, decorating these uniformly. Importantly, peptide coating did not suppress reactive oxygen species generation of TiO2 NPs, hence UV illumination triggered pronounced degradation of LPS and LTA by peptide-coated TiO2 NPs. Structural aspects of oxidative degradation were investigated by neutron reflectometry for smooth LPS, showing that degradation occurred preferentially in its outer O-antigen tails. Furthermore, cryo-TEM and light scattering showed lipopolysaccharide fragments resulting from degradation to be captured by the NP/LPS co-aggregates. The ability of LL-37-TiO2 NPs to capture and degrade LPS and LTA was demonstrated to be of importance for their ability to suppress lipopolysaccharide-induced activation in human monocytes at simultaneously low toxicity. Together, these results suggest that peptide-coated photocatalytic NPs offer opportunities for confinement of infection and inflammation.