Identification of genes encoding glycosyltransferases involved in lipopolysaccharide synthesis in Porphyromonas gingivalis

Summary

Porphyromonas gingivalis can synthesize both A-LPS and O-LPS, which contain anionic O-polysaccharides and conventional O-polysaccharides, respectively. A-LPS can anchor virulence proteins to the cell surface, and elucidating the mechanism of A-LPS synthesis is therefore important for understanding the pathogenicity of this bacterium. To identify the genes involved in LPS synthesis, we focused on uncharacterized genes encoding the glycosyltransferases, PGN_0361, PGN_ 1239, PGN_1240, and PGN_1668, which were tentatively named gtfC, gtfD, gtfE, and gtfF, respectively, and characterized their mutants. We found that disruption of gtfC and gtfF resulted in A-LPS deficiency. In addition, a gtfD mutant had abnormal A-LPS synthesis, and a gtfE mutant exhibited a rough-type LPS which possesses a short oligosaccharide with lipid A-core. We then constructed a gtfC and gtfD double mutant, since their amino acid sequences are very similar, and this mutant similarly possessed a rough-type LPS. Cross-complementation analysis revealed that the GtfD protein is a functional homolog of the Escherichia coli WbbL protein, which is a rhamnosyltransferase. These results suggested that the GtfE protein is essential for the synthesis of both O-LPS and A-LPS, and that GtfC and GtfD proteins may work together to synthesize the two kinds of LPS. In addition, the GtfF protein was essential for A-LPS synthesis, although this may be achieved in a strain-specific manner.

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