title: Structural insights into the histidine trimethylation activity of EgtD from Mycobacterium smegmatis.
abstract: EgtD is an S-adenosyl-l-methionine (SAM)-dependent histidine N,N,N-methyltransferase that catalyzes the formation of hercynine from histidine in the ergothioneine biosynthetic process of Mycobacterium smegmatis. Ergothioneine is a secreted antioxidant that protects mycobacterium from oxidative stress. Here, we present three crystal structures of EgtD in the apo form, the histidine-bound form, and the S-adenosyl-l-homocysteine (SAH)/histidine-bound form. The study revealed that EgtD consists of two distinct domains: a typical methyltransferase domain and a unique substrate binding domain. The histidine binding pocket of the substrate binding domain primarily recognizes the imidazole ring and carboxylate group of histidine rather than the amino group, explaining the high selectivity for histidine and/or (mono-, di-) methylated histidine as substrates. In addition, SAM binding to the MTase domain induced a conformational change in EgtD to facilitate the methyl transfer reaction. The structural analysis provides insights into the putative catalytic mechanism of EgtD in a processive trimethylation reaction.
authors.affiliation: Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, Republic of Korea.
authors.forename: Jae-Hee
authors.initials: JH
authors.lastname: Jeong
authors.affiliation: Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, Republic of Korea.
authors.forename: Hyung Jin
authors.initials: HJ
authors.lastname: Cha
authors.affiliation: Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, Republic of Korea.
authors.forename: Sung-Chul
authors.initials: SC
authors.lastname: Ha
authors.affiliation: Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, Republic of Korea.
authors.forename: Catleya
authors.initials: C
authors.lastname: Rojviriya
authors.affiliation: Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, Republic of Korea. Electronic address: ygkim76@postech.ac.kr.
authors.forename: Yeon-Gil
authors.initials: YG
authors.lastname: Kim
mesh_terms: D001622:Betaine / Q000031:analogs & derivatives* / Q000737:chemistry; D001665:Binding Sites; D006639:Histidine / Q000031:analogs & derivatives* / Q000737:chemistry*; D008745:Methylation; D008956:Models, Chemical; D008958:Models, Molecular; D020102:Mycobacterium smegmatis / Q000201:enzymology*; D011485:Protein Binding; D011487:Protein Conformation; D011496:Protein Methyltransferases / Q000737:chemistry* / Q000648:ultrastructure*; D017434:Protein Structure, Tertiary
chemical_list: D001622:Betaine; D006639:Histidine; D011496:Protein Methyltransferases; C007928:hercynine
keywords: Antioxidant; Crystal structure; Methyltransferase; Mycobacterium smegmatis; S-adenosyl-l-methionine