Identification and characterization of the ATP.Mg-dependent protein phosphatase activator (FA) as a microtubule protein kinase in the brain.
The activating factor of ATP.Mg-dependent protein phosphatase (FA) has been identified in brain microtubules. When using purified MAP-2 (microtubule associated protein 2) and tau proteins as substrates, FA could phosphorylate MAP-2 to 16 moles of phosphates per mole of protein with a Km value of 0.4 microM, and tau proteins to 4 moles of phosphates per mole of proteins with a Km value of about 3 microM. When using microtubules as substrates, FA could enhance many-fold the endogenous phosphorylation of many microtubule-associated proteins including MAP-2, tau proteins, and several low-molecular-weight MAPs. In contrast to other reported MAP kinases, such as cAMP-dependent protein kinase and Ca+2/phospholipid-dependent protein kinase, the FA-catalyzed phosphorylation of tau proteins could cause an electrophoretic mobility shift on sodium dodecyl sulfate polyacrylamide gel electrophoresis, suggesting that a dramatic conformational change of tau proteins was produced by FA. Peptide mapping analysis of the phosphopeptides derived from SV8 protease digestion revealed that FA could phosphorylate MAP-2 and tau proteins on at least four specific sites distinctly different from those phosphorylated by cAMP-dependent and Ca+2/phospholipid-dependent MAP kinases. Quantitative analysis further indicated that approximately 19% of the total endogenous kinase activity in brain microtubules was due to FA. Taken together, the results provide initial evidence that the ATP.Mg-dependent protein phosphatase activating factor (FA) is a potent and unique MAP kinase, and may represent one of the major factors involved in phosphorylation of brain microtubules.
Yang
S D
SD
Institute of Life Science, National Tsing Hua University, Hsinchu, Taiwan, Republic of China.
Yu
J S
JS
Lai
Y G
YG
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000201:enzymology / Q000648:ultrastructure*; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004789:Enzyme Activation / Q000187:drug effects; D008274:Magnesium / Q000494:pharmacology*; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008870:Microtubules / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism* / Q000494:pharmacology; D013552:Swine; D016875:tau Proteins / Q000378:metabolism
D008869:Microtubule-Associated Proteins; D016875:tau Proteins; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D008274:Magnesium