Cryo-EM structure of a methanogen nitrogenase-PII protein supercomplex.

Cryo-EM reveals a methanogen nitrogenase-PII supercomplex with three NifDK heterotetramers and six PII complexes, locking the enzyme in an inactive state.

• Why it matters: Understanding archaeal nitrogenase regulation is crucial because it differs from bacterial systems, and it plays a key role in the global nitrogen cycle, yet its structure and control mechanisms remain largely unknown.
• What they did: The study used cryo-electron microscopy to determine the native supercomplex structure from Methanosarcina acetivorans, showing PII complexes blocking NifH and coupling activity to energy and nitrogen signals.
• The result: Adding 2-oxoglutarate and ATP releases PII complexes, tripling NifDK activity in vitro, revealing a regulatory strategy that controls nitrogenase activity through higher-order assembly.