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Journal of Bacteriology, August 2007, p. 5515-5522, Vol. 189, No. 15
0021-9193/07/$08.00+0     doi:10.1128/JB.00344-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Characterization of the Fucosylation Pathway in the Biosynthesis of Glycopeptidolipids from Mycobacterium avium Complex

Department of Microbiology, Leprosy Research Center, National Institute of Infectious Diseases, 4-2-1 Aobacho, Higashimurayama, Tokyo 189-0002, Japan,¹ Japan BCG Central Laboratory, 3-1-5 Matsuyama, Kiyose, Tokyo 204-0022, Japan²

Received 3 March 2007/ Accepted 2 May 2007

The cell envelopes of several species of nontuberculous mycobacteria, including the Mycobacterium avium complex, contain glycopeptidolipids (GPLs) as major glycolipid components. GPLs are highly antigenic surface molecules, and their variant oligosaccharides define each serotype of the M. avium complex. In the oligosaccharide portion of GPLs, the fucose residue is one of the major sugar moieties, but its biosynthesis remains unclear. To elucidate it, we focused on the 5.0-kb chromosomal region of the M. avium complex that includes five genes, two of which showed high levels of similarity to the genes involved in fucose synthesis. For the characterization of this region by deletion and expression analyses, we constructed a recombinant Mycobacterium smegmatis strain that possesses the rtfA gene of the M. avium complex to produce serovar 1 GPL. The results revealed that the 5.0-kb chromosomal region is responsible for the addition of the fucose residue to serovar 1 GPL and that the three genes mdhtA, merA, and gtfD are indispensable for the fucosylation. Functional characterization revealed that the gtfD gene encodes a glycosyltransferase that transfers a fucose residue via 13 linkage to a rhamnose residue of serovar 1 GPL. The other two genes, mdhtA and merA, contributed to the formation of the fucose residue and were predicted to encode the enzymes responsible for the synthesis of fucose from mannose based on their deduced amino acid sequences. These results indicate that the fucosylation pathway in GPL biosynthesis is controlled by a combination of the mdhtA, merA, and gtfD genes. Our findings may contribute to the clarification of the complex glycosylation pathways involved in forming the oligosaccharide portion of GPLs from the M. avium complex, which are structurally distinct.

Published ahead of print on 25 May 2007.

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