Site-specific phosphorylation of synapsin I by mitogen-activated protein kinase and Cdk5 and its effects on physiological functions.
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.
Matsubara
M
M
Division of Biomedical Polymer Science, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-11, Japan.
Kusubata
M
M
Ishiguro
K
K
Uchida
T
T
Titani
K
K
Taniguchi
H
H
D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002417:Cattle; D002853:Chromatography, Liquid; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases; D003598:Cytoskeletal Proteins / Q000378:metabolism; D038341:Glycogen Synthase Kinases; D006868:Hydrolysis; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011392:Proline / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D016704:Synapsins / Q000378:metabolism*; D014404:Tubulin / Q000378:metabolism
D000199:Actins; D003598:Cytoskeletal Proteins; D016704:Synapsins; D014404:Tubulin; D011392:Proline; D038341:Glycogen Synthase Kinases; D051360:Cyclin-Dependent Kinase 5; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D018844:Cyclin-Dependent Kinases