O-GlcNAc Modification of Proteins

The covalent modification of protein side chains has been shown to be a fundamental mechanism by which information is transmitted and stored within the cell.  We are studying the covalent attachment of N-acetylglucosamine (GlcNAc) to serine and threonine residues of proteins in the brain.  This chemical modification shares many features with protein phosphorylation, which has been shown to underlie much of the communication between nerve cells.  Interestingly, a reciprocal relationship between protein phosphorylation and glycosylation has been observed in other tissues.  If O-GlcNAc addition modulates protein phosphorylation in nerve cells, this discovery would have profound implications for signal transduction in the brain.

We are using a combination of chemical and biological techniques to chart the O-GlcNAc proteome from several brain regions, including the hippocampus, a region involved in spatial learning, and the striatum, a region involved in motor control.  Dysfunctions in the striatum play critical roles in Parkinsonís and Huntingtonís disease.  Using state-of-the-art mass spectrometry techniques, we are studying numerous O-GlcNAc glycosylated proteins, including proteins involved in diverse cellular processes such as neurotransmitter release, neurite outgrowth and neuronal stress response.  We are currently in the process of identifying the sites of O-GlcNAc glycosylation on proteins of interest.

One of such proteins being investigated in our lab is cAMP response element binding protein (CREB), a transcription factor that plays crucial roles in learning and memory.    The phosphorylation of CREB by kinases regulated by cAMP enhances its  transcriptional activity and leads to long term changes in neuronal activity.  We have discovered that CREB contains multiple sites of O-GlcNAc glycosylation.  Glycosylation of CREB disrupts its interaction with the basal transcription machinery and represses gene expression.  We are further investigating the relationship between the phosphorylation and glycosylation of CREB in order to understand the functional significance of O-GlcNAc modification in neurons.