Overall fold of TkTrm10 constructs. (A) Crystal structure of TkTrm10Δ26 in cartoon representation. The α helices of the NTD and SPOUT domains are colored dark blue and light blue, respectively, while the β strands of the NTD and SPOUT domains are colored orange and light orange, respectively. The linker between the N-terminal and SPOUT domain is shown in pink. The three loop regions involved in forming the trefoil knot are shown in red and are labeled L1, L2, and L3. The missing regions of L2 and L3 are shown with red dotted curved lines. The SAM-binding pocket is indicated by an arrow. (B) Crystal structure of TkSPOUT_APO in cartoon representation. The missing L2 region is shown by a dotted red curved line. (C) Crystal structure of TkSPOUT_SAM in cartoon representation. The SAM molecule bound to the active site is shown as a stick model with carbon atoms colored yellow. The color code in panels B and C is the same as in A.