A New Structural Form in the SAM/Metal-Dependent O-Methyltransferase Family: MycE from the Mycinamicin Biosynthetic Pathway

JOURNAL OF MOLECULAR BIOLOGY

卷:413

Article

Akey, David L.¹  Li, Shengying¹  Konwerski, Jamie R.¹  Confer, Laura A.^1,2  Bernard, Steffen M.^1,3  Anzai, Yojiro⁴  Kato, Fumio⁴  Sherman, David H.^1,5,6,7  Smith, Janet L.^1,2 

[1] Univ Michigan, Inst Life Sci, Ann Arbor, MI 48109 USA

[2] Univ Michigan, Dept Biol Chem, Ann Arbor, MI 48109 USA

[3] Univ Michigan, Chem Biol Doctoral Program, Ann Arbor, MI 48109 USA

[4] Toho Univ, Fac Pharmaceut Sci, Chiba 2748510, Japan

[5] Univ Michigan, Dept Chem, Ann Arbor, MI 48109 USA

[6] Univ Michigan, Dept Med Chem, Ann Arbor, MI 48109 USA

[7] Univ Michigan, Dept Microbiol & Immunol, Ann Arbor, MI 48109 USA

关键词: metal-dependent methyltransfer;    antibiotic biosynthesis;    macrolide antibiotic;    S-adenosylmethionine-dependent methyltransfer;    methyltransferase;   

DOI  :  10.1016/j.jmb.2011.08.040

来源: Elsevier

【 摘 要 】

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. (C) 2011 Elsevier Ltd. All rights reserved.

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