Connor Blankenship, Pharmaceutical Sciences graduate student (Jiang Research Group), will be defending his PhD research thesis:

Uncovering the multifunctional roles of O-GlcNAc transferase’s cryptic intervening domain

The modification of intracellular proteins with O-linked β-N-acetylglucosamine (O-GlcNAc) moieties is a central mechanism of cellular nutrient sensing. In response to signals generated by the hexosamine biosynthetic pathway, this highly dynamic process spatiotemporally influences nearly every important cellular program. Additionally, aberrant O-GlcNAcylation has been observed in a range of diseases including cancer, neurodegeneration, and diabetes. Puzzlingly, this essential and abundant modification is regulated by a single pair of enzymes O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Despite its significance, little is known about OGT’s substrate recognition and regulation modes that allow it to recognize >8,000 protein substrates.

In this defense, I will discuss important discoveries in the substrate recognition and protein binding modes of OGT. We have identified the intervening domain (Int-D), a poorly understood protein fold found only in metazoan OGTs, as a specific regulator of OGT protein-protein interactions and substrate modification. Utilizing an innovative proteomic peptide phage display (ProP-PD) coupled with structural, biochemical, and cellular characterizations, we discovered a novel peptide binding motif. This sequence is recognized by the Int-D to facilitate specific O-GlcNAcylation and provide a pathway for crosstalk with tyrosine phosphorylation. We further show that disruption of Int-D binding dysregulates important cellular programs including response to nutrient deprivation and glucose metabolism. These findings illustrate a novel mode of OGT substrate recognition and offer the first insights into the biological roles of this unique intervening domain.