pmoB

PmoB is the large subunit of particulate methane monooxygenase (pMMO), the enzyme complex that catalyzes the aerobic oxidation of methane to methanol in many methanotrophic bacteria. It is encoded by the pmoB gene and is part of the pmoCAB operon, which also encodes the PmoA and PmoC subunits that together form the catalytic core.

PmoB has an estimated molecular mass around 60 kilodaltons and is primarily associated with the inner membrane, with portions exposed to the periplasm. In the canonical pMMO complex, PmoA, PmoB, and PmoC assemble to create a trimeric catalytic module embedded in the membrane, with PmoB contributing to the periplasmic region that participates in the enzyme’s chemistry.

The exact mechanism and active-site arrangement of pMMO remain areas of active research. Copper ions are strongly implicated in pMMO catalysis, and PmoB contains a copper-binding site within its periplasmic domain that is thought to contribute to the catalytic center or to electron transfer within the enzyme. The precise coordination environment and how it interfaces with the other subunits are topics of ongoing structural and biochemical studies.

Genetically, pmoB is conserved across diverse methanotrophs and is typically co-expressed with pmoA and pmoC as part of the operon. Changes in pmoB expression or sequence can influence methane oxidation efficiency, reflecting its essential role in the function of pMMO.

Structural studies have resolved portions of PmoB, revealing domain features consistent with copper binding and electron transfer. These findings contribute to the broader understanding of pMMO architecture and its catalytic mechanism, though a complete consensus on the active-site geometry continues to evolve.