Fig. 3: Conformational changes in MMUT and MMAA in the M₂C₂ complex.

A Overlay of MMUT in the M₂C₂ complex (blue) on free apo-MMUT (PDB: 3BIC) (dark grey) or with CoA (orange) and AdoCbl (maroon) bound (PDB:2XIQ) (light grey) shows that the B₁₂ ___domain is swung out by ~180° and is solvent exposed. In MMUT•AdoCbl an interconnecting belt (purple) wraps around the active site and protects the cofactor from solvent. In M₂C₂ the interconnecting belt is partially disordered (dark blue) B, C Comparison of free MMAA (PDB: 2WWW) (B) and MMAA in M₂C₂ (C), shows that it undergoes a large shift from an open to a closed conformation in the M₂C₂ complex, which leads to ordering of the switch I⁶² and III (pink) loops. D The MMAA active site in M₂C₂ shows that GDP (orange sticks) binding is stabilized by multiple hydrogen bonds as described in the text. Asp-270 and Glu-271 from the switch III loop of chain B (pink) also stabilize GDP binding. Mg²⁺ is coordinated by four oxygens donated by Ser-157, Glu-242, Asp-193, and oxygen from the β-phosphate of GDP. mFo-DFc omit map of GDP and Mg²⁺ at 2 σ is shown as a grey mesh.