Flat Solenoidal Ice-Binding Proteins as Scaffolds for Solid-Binders

Solid interfacing biomaterials is a crucial aspect of bionanotechnology and important for applications such as biosensing. Because of their potentially large contact area, flat solenoidal proteins are ideal scaffolds for designing proteins binding to surfaces of man-made solids such as minerals, metals, and plastics. To explore this opportunity, a naturally occurring flat solenoidal protein: the Rhagium inquistor Antifreeze Protein from the insect Rhagium inquisitor is re-designed. By mutating 4, 6, and 10 out of its 4 × 5 arrays of threonines into arginines, it have arrived at the silica-binding proteins RiSiBP-4, RiSiBP-6, and RiSiBP-10. Variants with increasing numbers of arginines bind stronger to silica, but are also less stable and increasingly difficult to produce. It is found that the RiSiBP-6 variant binds strongly to silica yet still has good stability and easy production. It is shown that sfGFP-RiSiBP-6 fusions allow for the functional display of a monolayer of sfGFP cargo on silica surfaces, suggesting the general usefulness of flat solenoidal proteins as scaffolds for designing solid-binding proteins.