Figure 4. Autoregulatory K-Loop of METTL16 Blocks the SAM Binding Pocket.

(A) Superimposition of MTD16-hp1x (as shown in Figure 1D) onto the structure of MTD16-SAH complex (PDB: 6B92) shown as pink cartoon representation. RMSD is 0.3 Å for 180 Cα atoms. SAH are shown as magenta sticks and labeled with a black arrow. K-loop region is indicated with a black dashed circle.

(B) Close-up view of the detailed interactions of the K-loop with the SAM binding pocket. Residues used in mutagenesis studies are shown in stick representation (blue, MTD16-hp1x; pink, MTD16-SAH). Black arrows highlight conformational differences.

(C) 2F_obs - F_calc map contoured at 1.0 σ for MTD16-hp1x is shown for a portion of the K-loop (blue sticks).

(D) In vitro methylation activity of wild-type or mutant METTL16 on hp1. Data are shown as mean DPM ± SD from three replicates.

(E) In vitro methylation activity over a range of SAM concentrations, with wild-type or mutant METTL16, for hp1. Data are shown as mean DPM ± SD from three replicates.

(F) In vitro methylation activity of wild-type or mutant METTL16 relative to the wild-type activity on the indicated RNA substrates. Data are shown as the ratio of the means, and error is ± the relative SD.

See also Figure S4.