Recently, we proved
the presence of sialylated N-glycans
using mass spectrometry in the tick salivary glands and the gut. We
proposed the host (blood) origin of these glycans and mapped the
transport of sialylated molecules from the gut to the salivary
glands. The sialylated molecules have been localized in specific
parts of the salivary glands suggesting specialized transport
mechanisms and functions in the physiology of the tick.
In the current
study, we performed quantification of sialylated molecules in tick
organs and tick cell cultures and compared the overall amount of
sialic acid to bioorthogonally labeled sialylated molecules.
Sialylated molecules were labeled by oxidation using sodium periodate
and a subsequent reaction with aminooxy-biotin, while metabolically
labeled sialic acid (using N-azido-mannosamine)
was labeled by biotin-alkyne through the Click reaction. Biotinylated
molecules were labeled either using streptavidin conjugated with
horseradish peroxidase (colorimetric quantification) or with a
fluorescent label (fluorescent microscopy). Gold conjugated antibody
to FITC was used to reveal metabolically labeled sialic acid using
electron microscopy.
Our results show
that the majority of sialylated molecules in the adult tick
originates in the host (blood) and are not synthesized by the tick.
In the tick cell cultures, bioorthogonally labeled structures were
not observed at all. Fluorescent microscopy analysis of tick organs
and tick cells corresponds with these results.
The absence of tick
sialylated molecules and the specific transport and localization of
host structures into the tick salivary glands and the saliva brings
many questions on the role of sialylated molecules in the physiology
and, specifically, the blood-feeding of ticks. Currently,
identification of these host proteins and of the transport mechanisms
is under.
