Biosynthetic lanthanide-luminescent mini-proteins using genetic code expansion

Non-canonical amino acids (ncAA) are promising as light-harvesting antennae for lanthanide luminescence in lanthanide-binding peptides and proteins. Here we present empirical insights into antenna-lanthanide interactions which reveal design principles of bright luminescent proteins. Peptides designed to act as lanthanide binding tags (LBT) show a trade-off between sensitization and lanthanide binding affinity. We generated a new protein, termed RF2, through computational design with nano-molar binding affinity and more than two-fold increase in terbium(III) luminescence. In this scaffold, 6-azatryptophan (6AW) achieved a ten-fold enhancement of the europium(III) luminescence in vivo . The RF2 6AW mutant also sensitizes the luminescence of dysprosium(III) and samarium(III). These results demonstrate the capability of de novo protein design to produce highly luminescent lanthanide-binding mini-proteins with a genetically encoded ncAA antenna.