Interaction of TiO 2 nanoparticles with proteins from aquatic organisms: the case of gill mucus from blue mussel

To better understand the mechanisms of TiO 2 nanoparticle (NP) uptake and toxicity in aquatic organisms, we investigated the interaction of NPs with the proteins found in gill mucus from blue mussels. Mucus is secreted by many aquatic organisms and is often their first line of defense against pathogens, xenobiotics, and other sources of environmental stress. Here, five TiO 2 NPs and one SiO 2 NP were incubated with gill mucus and run out on a one-dimensional polyacrylamide gel for a comparative qualitative analysis of the free proteins in the mucosal solution and the proteins bound to NPs. We then used nanoscale liquid chromatography coupled with tandem mass spectrometry to identify proteins of interest. Our data demonstrated dissimilar protein profiles between the crude mucosal solution and proteins adsorbed on NPs. In particular, extrapallial protein (EP), one of the most abundant mucus proteins, was absent from the adsorbed proteins. After thermal denaturation experiments, this absence was attributed to the EP content in aromatic amino acids that prevents protein unfolding and thus adsorption on the NP. Moreover, although the majority of the protein corona was qualitatively similar across the NPs tested here (SiO 2 and TiO 2 ), a few proteins in the corona showed a specific recruitment pattern according to the NP oxide (TiO 2 vs SiO 2 ) or crystal structure (anatase TiO 2 vs rutile TiO 2 ). Therefore, protein adsorption may vary with the type of NP. Graphical abstract Proteins with adsorption selectivity as identified from isolated bands