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

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• 作者：David L.  ; Akey¹ ; Shengying  ; Li¹ ; Jamie R.  ; Konwerski¹ ; Laura A.  ; Confer¹ ;   ; ² ; Steffen M.  ; Bernard¹ ;   ; ³ ; Yojiro  ; Anzai⁴ ; Fumio  ; Kato⁴ ; David H.  ; Sherman¹ ;   ; ⁵ ; Janet L.  ; Smith¹ ;   ; ² ;   ; ^{JanetSmith@umich.edu}
• 关键词：metal-dependent methyltransfer ; antibiotic biosynthesis ; macrolide antibiotic ; S-adenosylmethionine-dependent methyltransfer ; methyltransferase
• 刊名：Journal of Molecular Biology
• 出版年：2011
• 出版时间：21 October 2011
• 年：2011
• 卷：413
• 期：2
• 页码：438-450
• 全文大小：2106 K

文摘

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¨Cdisorder 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.