Identification and characterization of the ATP·Mg-dependent protein phosphatase activator (FA) as a microtubule protein kinase in the brain
- 1 April 1991
- journal article
- research article
- Published by Springer Nature in Protein Journal
- Vol. 10 (2) , 171-181
- https://doi.org/10.1007/bf01024781
Abstract
The activating factor of ATP·Mg-dependent protein phosphatase (F A) has been identified in brain microtubules. When using purified MAP-2 (microtubule associated protein 2) and tau proteins as substrates,F A could phosphorylate MAP-2 to 16 moles of phosphates per mole of protein with aK m value of 0.4 µM, and tau proteins to 4 moles of phosphates per mole of proteins with aK m value of about 3 µM. When using microtubules as substrates,F A 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, theF A-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 byF A. Peptide mapping analysis of the phosphopeptides derived from SV8 protease digestion revealed thatF A 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 toF A. Taken together, the results provide initial evidence that the ATP·Mg-dependent protein phosphatase activating factor (F A) is a potent and unique MAP kinase, and may represent one of the major factors involved in phosphorylation of brain microtubules.Keywords
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