Beyond Methane Oxidation: The Protein Landscape of ANME-2a Reveals an Integrated System for Diazotrophy and Membrane Fortification.

While renowned for mitigating methane emissions via anaerobic oxidation of methane (AOM), the full ecological strategy of ANME-2a archaea still requires further exploration. This study looks beyond methane oxidation to map the protein landscape of ANME-2a, revealing an integrated system for metabolic autonomy and environmental resilience in this specific isolate. Using a feature-based protein network derived from 230 Methanosarcinales genomes, we uncovered a sophisticated modular architecture. Key findings demonstrate that the AOM machinery is not isolated but functionally coupled with distinct modules dedicated to auxiliary functions. Our analysis not only confirms that this ANME-2a isolate possesses the complete genomic toolkit for autonomous diazotrophy but also reveals the molecular blueprint for its integration with AOM. We show how key machinery has been specialised to support the organism's core energy metabolism, with its core nitrogenase components co-clustered within the same functional module as AOM electron transfer proteins. Furthermore, we identified a specialised module dedicated to 'membrane fortification' through the significant enrichment of pathways for archaeal lipid biosynthesis. This modular blueprint, which integrates core energy metabolism with nitrogen fixation and structural lipid production, provides a model for how diazotrophic ANME-2a lineages may thrive as robust, self-sufficient organisms adapted to dynamic, resource-limited ecosystems.