The First Dipteran Luciferase From Keroplatus testaceus Evolved by Repurposing of a Storage Protein

Bioluminescence has independently evolved multiple times during animal evolution, yet the biochemical mechanisms underlying light production in true flies (Diptera) remain poorly understood. Here we describe the identification, cloning and functional characterization of the first dipteran luciferase from the fungus gnat Keroplatus testaceus. The 76‑kDa enzyme, KerLuc, is active when expressed heterologously in yeast, yielding a blue emission spectrum indistinguishable from native larvae. Sequence and domain analyses place the protein within the hemocyanin/hexamerin superfamily, but intriguingly, the protein lacks the canonical copper‑binding histidines. Structure prediction points to a hydrophobic cavity consistent with binding of the known Keroplatus oxyluciferin (3‑hydroxykynurenic acid), suggesting a novel catalytic mechanism. The luciferase is encoded by a single‑exon gene adjacent to a closely related paralogue within the conserved Enhancer of Split complex locus, indicating recent duplication and possible neofunctionalisation. Phylogenetic comparisons highlight proximity to Orfelia homologues and support independent origins of bioluminescence within Keroplatidae. Our results provide compelling evidence for a novel evolutionary origin for a luciferase from a storage protein, thereby closing a long-standing gap in understanding the molecular mechanisms of bioluminescence in Diptera.