Fig. 2: Binding of vitamin B₁₂ and S-adenosyl ligands by Mmp10.

a, The C8 side chain of MeCbl is shown in interaction with Y23, I220, L221 and N223 within the radical SAM domain, resulting in a planar tetrapyrrole ring. MeCbl has no lower axial ligand because it is pentacoordinated; however, L322, which resides at 3.9 Å from the cobalt atom, is part of a loop of residues forming a hydrophobic environment for the cobalt ion. Y23 appears at 4.8 Å from the cobalt ion. b,Snapshots of S-adenosyl cofactors within distinct Mmp10 structures. The distances between the sulfur atom of SAH and MTA or SAM and the cobalt ion are indicated by dashed lines. Top left, Mmp10 crystallized with SAH in the absence of peptide substrate (1: Mmp10 SAH structure; PDB 7QBV). Bottom left and top right, Mmp10 crystallized in the absence of substrate with SAM. Only the density of MTA was observed, which is labelled accordingly (2: Mmp10 MTA_1; PDB 7QBT; 3: Mmp10 MTA_2; PDB 7QBU). Bottom right, Mmp10 crystallized with SAM and its peptide substrate (4: Mmp10–SAM–peptide structure; PDB 7QBS). Light blue and purple, radical SAM domain residues; teal, cobalamin domain; green, SAM, MTA and SAH; magenta, MeCbl. The [4Fe–4S] cluster is shown as orange and yellow spheres. Omit maps (blue mesh) of ligands contoured at 3σ are depicted. See Extended Data Table 1 and Extended Data Fig. 4 for additional information.