[2P-1] Poster 2 (2P-01ー2P-37)

[2P-17] Structural insight into the activation mechanism with the structural change depending on SAM binding in histamine N-methyltransferase

^○Nonoka Godai^1,2, Kohei Takeshita¹, Naoki Sakai¹, Go Ueno¹, Sho Ito^1,2,3, Hideo Ago^1,2, Masaki Yamamoto^1,2 (1.RIKEN SPring-8 Center, 2.Grad., Scho, of Life Sci., Univ. of Hyogo, 3.Rigaku Corp)

Methyltransferases catalyzes the transfer of the methyl group from S-adenosyl-L-methionine (SAM) to several substrates. We previously proposed that the cysteine residue in the catalytic center of mouse DNA methyltransferase 1 (Dnmt1) flips to the ligand binding pocket only upon SAM binding. However, since the methyl group of SAM is easily desorbed spontaneously, it would be controversial whether the cysteine flip is substantial depended on SAM binding. Therefore, we validated the activation mechanism with structural change depending on SAM binding using human Histamine N-methyltransferase (hHNMT). We used hHNMT prepared by the insect cell expression system for crystal structure analysis. Unexpectedly, the purified hHNMT contained a endogenous histamine and the cysteine in the catalytic center does not face the ligand binding pocket, so referring to this structure would represented the post-methylation. On the other hand, hHNMT bound SAM crystal structure showed the cysteine was oriented toward the catalytic pocket. This SAM-dependent conformational change of hHNMT was similar to that suggested in the structural study of Dnmt1, supporting the importance of the cysteine residue flip mechanism as one of the activation mechanisms.