Figure 4.

Crystal structure of the human TGS1 protein. Trimethylguanosine synthase catalyzes hypermethylation of cap0 structure. In a 2-step reaction, 2 methyl groups are transferred to the amine group of m⁷G and, as a result, the m^2,2,7G structure is formed. The crystal structure of human TGS1 methyltransferase in complex with m⁷Gppp and SAH (shown in stick representation) is deposited in the PDB as 3GDH. Secondary structure elements that correspond to elements of the conserved RFM core are labeled. Secondary structure elements outside of the conserved core are not labeled.