Cytosolic O‐glycosylation is abundant in nerve terminals

Phosphorylation plays a key role in regulating growth cone migration and protein trafficking in nerve terminals. Here we show that nerve terminal proteins contain another abundant post‐translational modification: β‐ N ‐acetylglucosamine 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 phosphorylated proteins. We show that the activity and expression of O‐GlcNAc transferase (OGT) and N ‐acetyl‐β‐ d ‐glucosaminidase (O‐GlcNAcase), the two 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‐GlcNAc. Although most of these proteins are present in low abundance, we identified by proteomic analysis three neuron‐specific O‐GlcNAc modified proteins: collapsin response mediator protein‐2 (CRMP‐2), ubiquitin carboxyl hydrolase‐L1 (UCH‐L1) and β‐synuclein. CRMP‐2, which is involved in growth cone collapse, is a major O‐GlcNAc modified protein in synaptosomes. All three proteins are implicated in regulatory cascades that mediate intracellular signaling or neurodegenerative diseases. We propose that O‐GlcNAc modifications in the nerve terminal help regulate the functions of these and other synaptosome proteins, and that O‐GlcNAc may play a role in neurodegenerative disease.