Characterization of Protein Glycosylation in Francisellatularensis subsp. holarctica
2012
: FTH_0069 is a previously uncharacterized strongly
immunoreactive protein that has been proposed to be a novel
virulence factor in Francisella tularensis. Here, the glycan
structure modifying two C-terminal peptides of FTH_0069 was
identified utilizing high resolution, high mass accuracy mass
spectrometry, combined with in-source CID tandem MS
experiments. The glycan observed at m/z 1156 was determined to
be a hexasaccharide, consisting of two hexoses, three
N-acetylhexosamines, and an unknown monosaccharide containing a
phosphate group. The monosaccharide sequence of the glycan is
tentatively proposed as X-P-HexNAc-HexNAc-Hex-Hex-HexNAc, where
X denotes the unknown monosaccharide. The glycan is identical
to that of DsbA glycoprotein, as well as to one of the multiple
glycan structures modifying the type IV pilin PilA, suggesting
a common biosynthetic pathway for the protein
modification.Here, we demonstrate that the glycosylation of
FTH_0069, DsbA, and PilA was affected in an isogenic mutant
with a disrupted wbtDEF gene cluster encoding O-antigen
synthesis and in a mutant with a deleted pglA gene encoding
pilin oligosaccharyltransferase PglA. Based on our findings, we
propose that PglA is involved in both pilin and general F.
tularensis protein glycosylation, and we further suggest an
inter-relationship between the O-antigen and the glycan
synthesis in the early steps in their biosynthetic pathways.
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