Abstract:
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Trypanosoma brucei is the causative agent of human African
sleeping sickness and the cattle disease nagana. T. brucei is
dependent on glycoproteins for its survival and infectivity
throughout its life cycle. Here we report the functional
characterization of TbGT3, a glycosyltransferase expressed in
the bloodstream and procyclic-form of the parasite. Bloodstream
and procyclic-form TbGT3 conditional null mutants were created
and both exhibited normal growth under permissive and
non-permissive conditions. Under non-permissive conditions, the
normal glycosylation of the major glycoprotein of bloodstream
form T. brucei, the variant surface glycoprotein, and the
absence of major alterations in lectin binding to other
glycoproteins suggested that the major function of TbGT3 occurs
in the procyclic form of the parasite. Consistent with this, the
major surface glycoprotein of the procyclic form, procyclin,
exhibited a marked reduction in molecular weight due to changes
in glycosylphosphatidylinositol (GPI) anchor side-chains.
Structural analysis of the mutant procyclin GPI anchors
indicated that TbGT3 encodes a UDP-Gal: beta-GlcNAc-GPI beta1-3
Gal transferase. Despite the alterations in GPI anchor side
chains, TbGT3 conditional null mutants remained infectious to
tsetse flies under non-permissive conditions. |