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. 2022 Jun 29;61(32):e202204198. doi: 10.1002/anie.202204198

Figure 1.

Figure 1

The 2‐(S)‐methylglutamine modification within methyl‐coenzyme M reductase (MCR) is introduced by a cobalamin‐dependent radical SAM enzyme. a) Crystal structure of MCR from Methanothermobacter marburgensis (PDB ID 1MRO). The close‐up view of the active site of MCR on the right shows the modified amino acid 2‐(S)‐methylglutamine in yellow. The figure was prepared using PyMOL. b) A 28 amino acid peptide of the MCR α subunit from Methanoculleus thermophilus. The glutamine residue that is subjected to methylation is highlighted. The methylation reaction is proposed to be catalyzed by a cobalamin (Cbl)‐dependent radical SAM methyltransferase encoded by the SAMN04488571_10412 gene in M. thermophilus. c) General reaction mechanism proposed for class B radical SAM methyltransferases (modified from Zhang et al. 2012). SAM=S‐adenosyl‐l‐methionine, SAH=S‐adenosyl‐l‐homocysteine, DOA⋅=5′‐deoxyadenosyl radical, DOAH=5′‐deoxyadenosine, R⋅=substrate radical, RH=substrate.