Cytosolic O-glycosylation is abundant in nerve terminals

Phosphorylation plays a key role in regulating growth cone migration and pr otein trafficking in nerve terminals. Here we show that nerve terminal prot eins contain another abundant post-translational modification: beta -N-acet ylglucosamine linked to hydroxyls of serines or threonines (O-GlcNAc(1)). O -GlcNAc modifications are essential for embryogenesis and mounting evidence suggests that O-GlcNAc is a regulatory modification that affects many phos phorylated proteins. We show that the activity and expression of O-GlcNAc t ransferase (OGT) and N-acetyl-beta -D-glucosaminidase (O-GlcNAcase), the tw o enzymes regulating O-GlcNAc modifications, are present in nerve terminal structures (synaptosomes) and are particularily abundant in the cytosol of synaptosomes. Numerous synaptosome proteins are highly modified with O-GlcN Ac. Although most of these proteins are present in low abundance, we identi fied by proteomic analysis three neuron-specific O-GlcNAc modified proteins : collapsin response mediator protein-2 (CRMP-2), ubiquitin carboxyl hydrol ase-L1 (UCH-L1) and beta -synuclein. CRMP-2, which is involved in growth co ne collapse, is a major O-GlcNAc modified protein in synaptosomes. All thre e proteins are implicated in regulatory cascades that mediate intracellular signaling or neurodegenerative diseases. We propose that O-GlcNAc modifica tions in the nerve terminal help regulate the functions of these and other synaptosome proteins, and that O-GlcNAc may play a role in neurodegenerativ e disease.