Dual functionality of O -GlcNAc transferase is required for Drosophila development

Abstract

Post-translational modification of intracellular proteins with O-linked N-acetylglucosamine (O-GlcNAc) catalysed by O-GlcNAc transferase (OGT) has been linked to regulation of diverse cellular functions. OGT possesses a C-terminal glycosyltransferase catalytic domain and N-terminal tetratricopeptide repeats that are implicated in protein–protein interactions. Drosophila OGT (DmOGT) is encoded by super sex combs (sxc), mutants of which are pupal lethal. However, it is not clear if this phenotype is caused by reduction of O-GlcNAcylation. Here we use a genetic approach to demonstrate that post-pupal Drosophila development can proceed with negligible OGT catalysis, while early embryonic development is OGT activity-dependent. Structural and enzymatic comparison between human OGT (hOGT) and DmOGT informed the rational design of DmOGT point mutants with a range of reduced catalytic activities. Strikingly, a severely hypomorphic OGT mutant complements sxc pupal lethality. However, the hypomorphic OGT mutant-rescued progeny do not produce F2 adults, because a set of Hox genes is de-repressed in F2 embryos, resulting in homeotic phenotypes. Thus, OGT catalytic activity is required up to late pupal stages, while further development proceeds with severely reduced OGT activity.

A missense mutation in the catalytic domain of O‐GlcNAc transferase links perturbations in protein O‐GlcNAcylation to X‐linked intellectual disability

“…All other hormonal analysis and coagulation factors were in normal range. Immunological analysis showed repeatedly low percentage of activated T lymphocytes (1.4-2.1; normal 2.3-7.0 %) and mildly low CD8 T cells % (18%; normal [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. TIEF analysis of the serum has been repeatedly performed with normal profile result.…”

The Biochemistry of O-GlcNAc Transferase: Which Functions Make It Essential in Mammalian Cells?

“…Chromatin immunoprecipitation (112) and immunohistochemistry (113) demonstrated a high degree of overlap between signals for O-GlcNAcylated proteins and polycomb repressive complex 1, which was modified by O-GlcNAc on the core complex member polyhomeotic (Ph) (112). In subsequent studies, a catalytically inactive Asp-to-Ala mutant of Ogt produced live adults when wild-type maternal Ogt was present to get past embryogenesis (123). This variant, which eliminates a hydrogen bond between the ribose of UDP-GlcNAc and the active site, displays no detectable activity in vitro.…”

“…This finding supports the idea that O-GlcNAc may be dispensable in the adult fly. However, other catalytically inactive OGT variants do not produce live adults, and it has been speculated that the Asp-to-Ala mutant may have residual catalytic activity (112,113,123). Gambetta & Müller (124) have proposed a mechanism for how OGT mediates polycomb repression in flies.…”

O-GlcNAc transferase missense mutations linked to X-linked intellectual disability deregulate genes involved in cell fate determination and signaling

“…OGT interacts with a number of proteins in the cell through its N-terminal TPRs (44). Although the TPRs are also implicated in the recognition of certain substrates for O-GlcNAcylation (15), it has been shown using hypomorphic OGT mutants of the fly that post-pupal development proceeds in the near-absence of the catalytic activity of OGT (45), suggesting that the scaffolding function of OGT in forming functional protein complexes is also critical. Given that the XLID mutations lie in the TPR domain of OGT, we also hypothesize that an altered OGT-interactome in these patients may be responsible for disease and are in the process of defining the differential OGT-interactome using multiple parallel…”