Site-specific phosphorylation of synapsin I by mitogen-activated protein kinase and Cdk5 and its effects on physiological functions

J Biol Chem. 1996 Aug 30;271(35):21108-13. doi: 10.1074/jbc.271.35.21108.


Posttranslational modifications of synapsin I, a major phosphoprotein in synaptic terminals, were studied by mass spectrometry. In addition to a well known phosphorylation site by calmodulin-dependent protein kinase II (CaM kinase II), a hitherto unrecognized site (Ser553) was found phosphorylated in vivo. The phosphorylation site is immediately followed by a proline, suggesting that the protein is an in vivo substrate of so-called proline-directed protein kinase(s). To identify the kinase involved, three proline-directed protein kinases expressed highly in the brain, i.e. mitogen-activated protein (MAP) kinase, Cdk5-p23, and glycogen synthase kinase 3beta, were tested for the in vitro phosphorylation of synapsin I. Only MAP kinase and Cdk5-p23 phosphorylated synapsin I stoichiometrically. The phosphorylation sites were determined to be Ser551 and Ser553 with Cdk5-p23, and Ser62, Ser67, and Ser551 with MAP kinase. Upon phosphorylation with MAP kinase, synapsin I showed reduced F-actin bundling activity, while no significant effect on the interaction was observed with the protein phosphorylated with Cdk5-p23. These results raise the possibility that the so-called proline-directed protein kinases together with CaM kinase II and cAMP-dependent protein kinase play an important role in the regulation of synapsin I function.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism
  • Amino Acid Sequence
  • Animals
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism*
  • Cattle
  • Chromatography, Liquid
  • Cyclin-Dependent Kinase 5
  • Cyclin-Dependent Kinases*
  • Cytoskeletal Proteins / metabolism
  • Glycogen Synthase Kinases
  • Hydrolysis
  • Mass Spectrometry
  • Molecular Sequence Data
  • Phosphorylation
  • Proline / metabolism
  • Protein Binding
  • Protein-Serine-Threonine Kinases / metabolism*
  • Synapsins / metabolism*
  • Tubulin / metabolism


  • Actins
  • Cytoskeletal Proteins
  • Synapsins
  • Tubulin
  • Proline
  • Glycogen Synthase Kinases
  • Cyclin-Dependent Kinase 5
  • Protein-Serine-Threonine Kinases
  • Calcium-Calmodulin-Dependent Protein Kinases
  • Cyclin-Dependent Kinases