Catalytic and inhibitory architecture of comammox ammonia monooxygenase

Complete ammonia oxidizers (comammox) are widespread nitrifiers that can dominate ammonia oxidation in diverse environments by efficiently converting ammonia to nitrate within a single cell, yet the molecular basis distinguishing their ammonia monooxygenase (AMO) from those of canonical bacterial AMO remains unresolved. Here we report cryo-electron microscopy (cryo-EM) structures of AMO from the comammox Nitrospira inopinata ( Ni AMO) in inhibitor-free and allylthiourea (ATU)-bound states at 2.47 Å and 2.68 Å resolution, respectively. Ni AMO displays distinctive auxiliary-subunit organization, copper-site configuration and hydrophobic-channel architecture. Integrative molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) calculations support a methyl-plastoquinol (methyl-PQH ₂ )-coupled, Cu _D -centric catalytic model, with Cu _C potentially facilitating quinone redox cycling. N. inopinata exhibited broad susceptibility to several known nitrification inhibitors, and ATU-bound Ni AMO structure localized the inhibitor to the Cu _C –Cu _D region, accompanied by constriction of the hydrophobic channel, which is consistent with the competitive role of ATU demonstrated in recovery assays. Multi-omics analyses further revealed an energy-limited stress response to ATU, including induction of urea transport and utilization systems. Collectively, these findings define a methyl-PQ-linked catalytic and inhibitor-responsive architecture of comammox AMO and establish a mechanistic framework for lineage-aware management of nitrification in natural and engineered ecosystems.