Structure and Mechanism of the Azomycin Biosynthetic Enzyme RohQ That Catalyzes a Spontaneous Cyclodehydration

RohQ from the azomycin biosynthetic pathway catalyzes a spontaneous cyclodehydration to form 2-aminoimidazole. Here we report the structure and mechanism of RohQ and use a serendipitously bound imidazole to pinpoint active site residues. We propose that catalysis occurs at the dimeric interface using two key aspartic acid residues for proton transfer steps to accelerate 3 × 10⁴-fold intramolecular cyclization of a guanidino group and aldehyde, releasing water. Our work expands our understanding of de novo emerged enzymes and provides the first structural and mechanistic view of a yet-unexplored protein family.