title: A new structural form in the SAM/metal-dependent o‑methyltransferase family: MycE from the mycinamicin biosynthetic pathway.
abstract: O-linked methylation of sugar substituents is a common modification in the biosynthesis of many natural products and is catalyzed by multiple families of S-adenosyl-L-methionine (SAM or AdoMet)-dependent methyltransferases (MTs). Mycinamicins, potent antibiotics from Micromonospora griseorubida, can be methylated at two positions on a 6-deoxyallose substituent. The first methylation is catalyzed by MycE, a SAM- and metal-dependent MT. Crystal structures were determined for MycE bound to the product S-adenosyl-L-homocysteine (AdoHcy) and magnesium, both with and without the natural substrate mycinamicin VI. This represents the first structure of a natural product sugar MT in complex with its natural substrate. MycE is a tetramer of a two-domain polypeptide, comprising a C-terminal catalytic MT domain and an N-terminal auxiliary domain, which is important for quaternary assembly and for substrate binding. The symmetric MycE tetramer has a novel MT organization in which each of the four active sites is formed at the junction of three monomers within the tetramer. The active-site structure supports a mechanism in which a conserved histidine acts as a general base, and the metal ion helps to position the methyl acceptor and to stabilize a hydroxylate intermediate. A conserved tyrosine is suggested to support activity through interactions with the transferred methyl group from the SAM methyl donor. The structure of the free enzyme reveals a dramatic order-disorder transition in the active site relative to the S-adenosyl-L-homocysteine complexes, suggesting a mechanism for product/substrate exchange through concerted movement of five loops and the polypeptide C-terminus.
authors: Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA.
authors: David L
authors: DL
authors: Akey
authors: Shengying
authors: S
authors: Li
authors: Jamie R
authors: JR
authors: Konwerski
authors: Laura A
authors: LA
authors: Confer
authors: Steffen M
authors: SM
authors: Bernard
authors: Yojiro
authors: Y
authors: Anzai
authors: Fumio
authors: F
authors: Kato
authors: David H
authors: DH
authors: Sherman
authors: Janet L
authors: JL
authors: Smith
mesh_terms: D000595:Amino Acid Sequence; D053898:Biosynthetic Pathways; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D018942:Macrolides / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D008780:Methyltransferases / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D012435:S-Adenosylhomocysteine / Q000378:metabolism*
chemical_list: D018942:Macrolides; D021122:Protein Subunits; C026686:mycinamicins; D012435:S-Adenosylhomocysteine; D008780:Methyltransferases; D008274:Magnesium