Fig. 4: MMUT-MMAA interfaces.

A Each MMUT subunit comprising the substrate- (blue) and B₁₂ (cyan) domains and the inter-connecting belt (dark blue) in M₂C₂ interacts with an MMAA dimer (yellow ribbons). CoA (orange) and GDP (orange) are shown as spheres. Boxes (dashed lines) outline two MMUT-MMAA interfaces. B Close-up of the MMUT substrate domain (blue) and MMAA (chain A, yellow) interface. Black dashed lines represent interactions between residues on MMUT and MMAA (chain A) as described in the text. C, D Close-up of the interface between the B₁₂ domain and MMAA (chain B). C Switch I on MMAA (green) is ordered, forming a short β-strand and hydrogen bonds with the terminal β-strand in the B₁₂ domain, resulting in an extended β-sheet interaction between the two proteins. Salt bridge and hydrogen bond interactions are shown with dashed lines. D Additional interactions (dashed black line) between MMAA and MMUT residues stabilize the B₁₂ domain-MMAA interface as described in the text.