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

Robert N. Cole, Gerald W. Hart

Research output: Contribution to journalArticlepeer-review

Abstract

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 K(m) of calcium/calmodulin-dependent protein kinase II phosphorylation of site Ser566 with no effect on its V(max). We conclude that O-GlcNAcylation likely plays a more direct role in synapsin I interactions than simply modulating the protein's phosphorylation.

Original languageEnglish (US)
Pages (from-to)418-428
Number of pages11
JournalJournal of Neurochemistry
Volume73
Issue number1
DOIs
StatePublished - 1999

Keywords

  • Calcium/Calmodulin-dependent protein kinase II
  • Cytoskeleton
  • Mass spectrometry
  • O-GlcNAcylation
  • Posttranslational modification
  • Synapse

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience

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