Understanding the relationships between solubility, stability, and activity of silicatein

Abstract

Silicatein is an enzyme that mineralizes environmental precursors to patterned nanomaterials and is found naturally orchestrating the complex and beautiful exoskeletons of marine sponges. To harness this activity for nanomaterial biomanufacturing, enzyme solubility and stability have been widely studied. We address the enzyme's solubility challenge via protein fusion tags: enhanced green fluorescent protein (eGFP), monomeric superfolder GFP (msGFP2), and trigger factor (TF). All three silicatein fusion proteins form oligomers to varying degrees, that are partially modulated by disulfide bridges. Biomineralization activity was assessed with silica and nanoceria, showing comparable yields for eGFP-silicatein and TF-silicatein, as well as identical composition of mineralized products regardless of disulfide bridge reduction, shown via XRD characterization of silicatein's nanocrystalline product. This implies that solubility has only minor effects on silicatein activity and that continued improvement in this area is currently inessential. Furthermore, these results suggest that silicatein biomineralization activity is inherent to the enzyme itself. Thus, future studies should be aimed at understanding silicatein's kinetic mechanisms.