Fig. 2: The three-dimensional structure of PsiM in complex with SAH and norbaeocystin.
a Ribbon representation of the orthorhombic crystal structure at 0.91 Å resolution (PDB 8PB4). The Rossmann fold is depicted in beige, the N-terminal jaw-like domain in blue and two helices forming a unique C-terminal extension in red. The region 189–221, which bears no homology to other methyltransferases and acts as a substrate recognition loop (SRL), is coloured green. SAH and norbaeocystin are represented as yellow and pink space-filling models, respectively. The N-terminal extension preceding the jaw domain (shown in grey) mainly consists of a TEV protease site originating from the expression vector. b Topology diagram for the PsiM fold (colours as in a). c Wall-eyed stereo figure showing OMIT density for the two ligands in the monoclinic crystal form, PDB 8PB3 (2mFo-DFc with SAH and norbaeocystin omitted simultaneously, map contoured at 1.0 σ). Also shown are functionally relevant protein residues (stick models) and key hydrogen bonds (dashed lines). An arrow indicates the direction of the nucleophilic attack.
