O-linked β-N-acetylglucosamine (O-GlcNAc) glycosylation
is an important post-translational modification in many
cellular processes. It is mediated by O-GlcNAc transferases
(OGTs), which catalyze the addition of O-GlcNAc to serine
or threonine residues of the target proteins. In this study,
we expressed a putative Yarrowia lipolytica OGT (YlOGT),
the only homolog identified in the subphylum Saccharomycotina
through bioinformatics analysis, and the human OGT
(hOGT) as recombinant proteins in Saccharomyces cerevisiae,
and performed their functional characterization. Immunoblotting
assays using antibody against O-GlcNAc revealed that
recombinant hOGT (rhOGT), but not the recombinant YlOGT
(rYlOGT), undergoes auto-O-GlcNAcylation in the heterologous
host S. cerevisiae. Moreover, the rhOGT expressed
in S. cerevisiae showed a catalytic activity during in vitro assays
using casein kinase II substrates, whereas no such activity
was obtained in rYlOGT. However, the chimeric human-Y.
lipolytica OGT, carrying the human tetratricopeptide repeat
(TPR) domain along with the Y. lipolytica catalytic domain
(CTD), mediated the transfer of O-GlcNAc moiety during
the in vitro assays. Although the overexpression of full-length
OGTs inhibited the growth of S. cerevisiae, no such inhibition
was obtained upon overexpression of only the CTD fragment,
indicating the role of TPR domain in growth inhibition.
This is the first report on the functional analysis of the
fungal OGT, indicating that the Y. lipolytica OGT retains
its catalytic activity, although the physiological role and substrates
of YlOGT remain to be elucidated.
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