Identification of the ATP.Mg-dependent protein phosphatase activator (FA) as a synapsin I kinase that inhibits cross-linking of synapsin I with brain microtubules.
The ATP.Mg-dependent protein phosphatase activating factor (FA) has been identified and purified to near homogeneity from brain. In this report, as evidenced on SDS-polyacrylamide gel electrophoresis followed by autoradiography, factor FA has further been identified as a cAMP and Ca(2+)-independent brain kinase that could phosphorylate synapsin I, a neuronal protein that coats synaptic vesicles, binds to cytoskeleton, and is believed to be involved in the modulation of neurotransmission. Kinetic study further indicated that factor FA could phosphorylate synapsin I with a low Km value of about 2 microM and with a molar ratio of 1 mol of phosphate per mole of protein. Peptide mapping analysis revealed that factor FA specifically phosphorylated the tail region of synapsin I but on a unique site distinct from those phosphorylated by Ca2+/calmodulin-dependent protein kinase II and cAMP-dependent protein kinase, the two well-established synapsin I kinases. Functional study further revealed that factor FA could phosphorylate this unique specific site on the tail region of synapsin I and thereby inhibit cross-linking of synapsin I with microtubules. The results further suggest the possible involvement of factor FA as a synapsin I kinase in the regulation of axonal transport process of synaptic vesicles via the promotion of vesicles motility during neurotransmission.
Yang
S D
SD
Institute of Biomedical and Life Science, National Tsing Hua University, Hsinchu, Taiwan, ROC.
Song
J S
JS
Hsieh
Y T
YT
Liu
H W
HW
Chan
W H
WH
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000648:ultrastructure*; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008870:Microtubules / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000494:pharmacology*; D011817:Rabbits; D013552:Swine; D016704:Synapsins / Q000378:metabolism*; D014404:Tubulin / Q000378:metabolism
D016704:Synapsins; D014404:Tubulin; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D008274:Magnesium