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Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
Reprint requests to: John S. Blanchard, Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA; e-mail: blanchar{at}aecom.yu.edu; fax: (718) 430-8565.
Mycothiol is the predominant low-molecular weight thiol produced by actinomycetes, including Mycobacterium tuberculosis. The last reaction in the biosynthetic pathway for mycothiol is catalyzed by mycothiol synthase (MshD), which acetylates the cysteinyl amine of cysteineglucosamineinositol (CysGlcNIns). The crystal structure of MshD was determined in the presence of coenzyme A and acetylCoA . MshD consists of two tandem-repeated domains, each exhibiting the Gcn5-related N-acetyltransferase (GNAT) fold. These two domains superimpose with a root-mean-square deviation of 1.7 Å over 88 residues, and each was found to bind one molecule of coenzyme, although the binding sites are quite different. The C-terminal domain has a similar active site to many GNAT members in which the acetyl group of the coenzyme is presented to an open active site slot. However, acetylCoA bound to the N-terminal domain is buried, and is apparently not positioned to promote acetyl transfer. A modeled substrate complex indicates that CysGlcNIns would only fill a portion of a negatively charged channel located between the two domains. This is the first structure determined for an enzyme involved in the biosynthesis of mycothiol.
Keywords: Mycothiol biosynthesis; GNAT fold; acetyltransferase
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