The Role of the O‐GlcNAc Transferase Interactome in X‐linked Intellectual Disability

Abstract

Both Ser/Thr phosphorylation and O‐linked beta‐N‐acetylglucosamine (O‐GlcNAc) modification occurs on thousands of nuclear and cytosolic proteins. The forces of evolution have resulted in gene duplication and divergence of substrate recognition for kinases to gain specificity. However there is only one mammalian gene encoding the O‐GlcNAc transferase (OGT). Missense mutations in this gene have been established as being causal for X‐linked intellectual disability. Working with collaborators, we have characterized several of the resulting OGT variants and found little to no defects in global O‐GlcNAc levels, enzyme kinetics, or stability. This led us to consider how is OGT regulated and targeted to substrates and whether the XLID associated variants had defects in protein‐protein interactions.It has been suggested that the N‐terminal tetratricopeptide repeat (TPR) domain of OGT, where many XLID variants occur, rather than its C‐terminal catalytic domain, is responsible for OGT substrate selection by targeting to specific complexes and subcompartments of the cell. To assess the role of the TPR domain in OGT protein interaction, we generated a BioID proximity proteomics system. Utilizing a fusion protein, TPR‐BirA*, has allowed us to identify more than 100 OGT TPR domain‐interacting proteins. We also utilized BioID to identify proteins that fail to interact with the OGT XLID variants and are in the process of identifying cell type specific differences in protein:protein interactions of the variants focusing on neural lineages. This screen to date has already produced several candidates known to be involved in neurodevelopmental disorders that represent potential mechanisms for how OGT mutations could lead to XLID. These candidates set the stage for future work elucidating the function of specific OGT TPR interactions and how they contribute to OGT function and pathophysiology.Support or Funding InformationThis work is supported in part by NICHD/NIH (R21HD097652)