Glycosylation sites flank phosphorylation sites on synapsin I: O-linked N-acetylglucosamine residues are localized within domains mediating synapsin I interactions

J Neurochem. 1999 Jul;73(1):418-28. doi: 10.1046/j.1471-4159.1999.0730418.x.


Synapsin I is concentrated in nerve terminals, where it appears to anchor synaptic vesicles to the cytoskeleton and thereby ensures a steady supply of fusion-competent synaptic vesicles. Although phosphorylation-dependent binding of synapsin I to cytoskeletal elements and synaptic vesicles is well characterized, little is known about synapsin I's O-linked N-acetylglucosamine (O-GlcNAc) modifications. Here, we identified seven in vivo O-GlcNAcylation sites on synapsin I by analysis of HPLC-purified digests of rat brain synapsin I. The seven O-GlcNAcylation sites (Ser55, Thr56, Thr87, Ser516, Thr524, Thr562, and Ser576) in synapsin I are clustered around its five phosphorylation sites in domains B and D. The proximity of phosphorylation sites to O-GlcNAcylation sites in the regulatory domains of synapsin I suggests that O-GlcNAcylation may modulate phosphorylation and indirectly affect synapsin I interactions. With use of synthetic peptides, however, the presence of an O-GlcNAc at sites Thr562 and Ser576 resulted in only a 66% increase in the Km of calcium/calmodulin-dependent protein kinase II phosphorylation of site Ser566 with no effect on its Vmax. We conclude that O-GlcNAcylation likely plays a more direct role in synapsin I interactions than simply modulating the protein's phosphorylation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetylglucosamine / analysis*
  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism
  • Carbohydrate Conformation
  • Chromatography, High Pressure Liquid
  • Glycosylation
  • Mass Spectrometry
  • Molecular Sequence Data
  • Peptide Fragments / chemistry
  • Peptide Fragments / isolation & purification
  • Phosphorylation
  • Rats
  • Rats, Sprague-Dawley
  • Synapsins / chemistry*
  • Synapsins / metabolism*


  • Peptide Fragments
  • Synapsins
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2
  • Calcium-Calmodulin-Dependent Protein Kinases
  • Acetylglucosamine