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Glycosylation Sites Flank Phosphorylation Sites on Synapsin I
Author(s) -
Cole Robert N.,
Hart Gerald W.
Publication year - 1999
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1999.0730418.x
Subject(s) - synapsin i , synapsin , phosphorylation , synaptic vesicle , biology , protein phosphorylation , biochemistry , microbiology and biotechnology , protein kinase a , chemistry , biophysics , vesicle , membrane
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 (Ser 55 , Thr 56 , Thr 87 , Ser 516 , Thr 524 , Thr 562 , and Ser 576 ) 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 Thr 562 and Ser 576 resulted in only a 66% increase in the K m of calcium/calmodulin‐dependent protein kinase II phosphorylation of site Ser 566 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.