In vitro gene expression and enzyme catalysis in bio-inorganic protocells

Silica nanoparticles with a balance of hydrophilic and hydrophobic surface properties exhibit surfactant-like behaviour, and as a consequence can strongly adsorb at oil/water interfaces to stabilize the formation of water micro-droplets. Here we exploit this strategy to construct a model of a primitive bio-inorganic protocell, which unlike conventional paradigms based on self-assembled vesicles, is structurally delineated by a porous inorganic membrane rather than a lipid-based bilayer. As proof-of-principle we show that the nanoparticle-stabilized droplets (colloidosomes) can support a range of functionally active biomolecules and bio-machinery related to metabolic and informational processing. Specifically, we demonstrate that the rate of cell-free in vitro gene expression of enhanced green fluorescent protein (eGFP) is essentially the same within the colloidosome interior as in bulk aqueous solution. In addition, we report considerable enhancements in the specific activity of enzymes such as lipoprotein lipase, chymotrypsin or alkaline phosphatase when entrapped within the nanoparticle-stabilized water droplets. Our results suggest that artificial protocells based on the construction of biological/inorganic nanoscale components could have considerable potential in areas such as synthetic biology and bionanotechnology. In a wider perspective, studies on bio-inorganic protocells could provide alternative models for evaluating potential prebiotic pathways prior to the emergence of lipid-based compartmentalization on the early Earth.