text: In Chaetomium thermophilum, a complex of a metabolon exists between fatty acid synthase and a MDa carboxylase, and was observed using chemical cross-linking coupled to mass spectrometry and visualized by cryo-electron microscopy. The Fatty acid synthesis metabolon in C. thermophilum is highly flexible, and although a high-resolution structure of Fatty acid synthase was possible, the metabolon was highly flexible, hindering high-resolution structure determination.