Abstract
<title>Abstract</title> <p>Cryptochrome/photolyase-family proteins are flavin adenine dinucleotide-dependent blue-light proteins involved in DNA repair, light sensing and electron-transfer chemistry. Radical-pair photochemistry has been demonstrated in bacterial Escherichia coli cyclobutane pyrimidine dimer photolyase, but the broader bacterial diversity of radical-pair-relevant architectures remains poorly explored. Here, we screened 22,081 bacterial cryptochrome/photolyase-family proteins and refined them to 5,016 domain-supported, species-deduplicated candidates spanning cyclobutane pyrimidine dimer photolyases, cryptochrome-like proteins, cryptochrome DASH proteins and 6–4 photolyases. Structural and graph-based analysis identified A0A6M1RS91, a cyclobutane pyrimidine dimer photolyase from the thermophilic bacterium Limisphaera ngatamarikiensis, as the strongest candidate. Compared with the E. coli benchmark, A0A6M1RS91 contained 31 versus 15 total tryptophans, 12 versus 7 flavin-proximal tryptophans within 12 Å, 24 versus 9 flavin-connected tryptophans, and 73 versus 33 predicted flavin-to-tryptophan paths. Its best predicted route was flavin adenine dinucleotide to phenylalanine 373, tryptophan 389, tryptophan 323 and tryptophan 372, indicating an expanded aromatic network around the flavin site. These results move bacterial radical-pair discovery beyond model photolyases and identify A0A6M1RS91 as a focused experimental target for testing flavin photoreduction, flavin–tryptophan radical formation and magnetic-field-sensitive photochemistry.</p>