Quantitative mapping of microtubule-associated protein 2c (MAP2c) phosphorylation and regulatory protein 14-3-3ζ-binding sites reveals key differences between MAP2c and its homolog Tau.

Microtubule-associated protein 2c (MAP2c) is involved inneuronal development and is less characterized than its homologTau, which has various roles in neurodegeneration. Using NMRmethods providing single-residue resolution and quantitativecomparison, we investigated molecular interactions importantfor the regulatory roles of MAP2c in microtubule dynamics. Wefound that MAP2c and Tau significantly differ in the positionand kinetics of sites that are phosphorylated by cAMP-dependentprotein kinase (PKA), even in highly homologous regions.Wedetermined the binding sites of unphosphorylated andphosphorylated MAP2c responsible for interactions with theregulatory protein 14-3-3 zeta. Differences in phosphorylationand in charge distribution between MAP2c and Tau suggested thatboth MAP2c and Tau respond to the same signal (phosphorylationby PKA) but have different downstream effects, indicating asignaling branch point for controlling microtubule stability.Although the interactions of phosphorylated Tau with 14-3-3zeta are supposed to be a major factor in microtubuledestabilization, the binding of 14-3-3 zeta to MAP2c enhancedby PKA-mediated phosphorylation is likely to influencemicrotubule-MAP2c binding much less, in agreement with theresults of our tubulin co-sedimentation measurements. Thespecific location of the major MAP2c phosphorylation site in aregion homologous to the muscarinic receptor-binding site ofTau suggests that MAP2c also may regulate processes other thanmicrotubule dynamics.