Natural product biosynthesis by guanidine prenyltransferases in plants and bacteria

Guanidine exists almost exclusively as a resonance-stabilized cation, making its direct enzymatic functionalization challenging. We identified the cyanobacterial enzyme NosH, which catalyzes direct prenyl transfer to free guanidine. Structural and mechanistic analyses revealed guanidine activation by a two-aspartate clamp coupled to prenyl-donor binding through a distinct catalytic architecture. Guided by these features, we identified a large family of guanidine prenyltransferases across bacteria and plants. Plant enzymes produced guanidine alkaloids such as galegine in vitro and heterologous expression of a plant ortholog in Nicotiana benthamiana produced galegine in planta, providing a direct enzymatic link to plant-specialized metabolism.