RNA-stabilized protein nanorings: high-precision adapters for biohybrid design

The equipment of technical devices with biogenic adapter structures enables effective integration of biofunctional units into advanced sensor, filtration or catalytic layouts. Plant virus-derived self-organizing supramolecular complexes are among the most promising soft-matter adapters due to their multivalence on the nanometer scale, precise dimensions, high availability and compatibility with routine conjugation chemistry. Bioengineering can tailor both the templates’ shapes and coupling sites and has been applied here to develop nucleoprotein ‘nanorings’ made of tobacco mosaic virus (TMV) building blocks. Short RNA-scaffolded four-turn helices of ≈68 protein subunits and ≈9 nm length, with 18 nm outer and 4 nm inner diameters, were generated efficiently in vitro. A structure-directing single-stranded 204-nucleotide ribonucleic acid containing the TMV origin of assembly-yielded colloidal preparations that have structural integrity and are well dispersed in a pH range from about 7 to 9. Two selectively addressable protein types with either an amino or a thiol group accessible were combined in the ring-like objects, allowing dual covalent coupling of a fluorescent dye first and to an isothiocyanate-covered substrate thereafter. Such precisely shaped nanoconstructs with distinct functional groups exposed in high surface densities offer novel opportunities as versatile adapter elements for the fabrication of extended bio/synthetic hybrid materials.