Edited by Norma AllewellMicrotubule-associated protein 2c (MAP2c) is involved in neuronal development and is less characterized than its homolog Tau, which has various roles in neurodegeneration. Using NMR methods providing single-residue resolution and quantitative comparison, we investigated molecular interactions important for the regulatory roles of MAP2c in microtubule dynamics. We found that MAP2c and Tau significantly differ in the position and kinetics of sites that are phosphorylated by cAMP-dependent protein kinase (PKA), even in highly homologous regions. We determined the binding sites of unphosphorylated and phosphorylated MAP2c responsible for interactions with the regulatory protein 14-3-3 . Differences in phosphorylation and in charge distribution between MAP2c and Tau suggested that both MAP2c and Tau respond to the same signal (phosphorylation by PKA) but have different downstream effects, indicating a signaling branch point for controlling microtubule stability. Although the interactions of phosphorylated Tau with 14-3-3 are supposed to be a major factor in microtubule destabilization, the binding of 14-3-3 to MAP2c enhanced by PKA-mediated phosphorylation is likely to influence microtubule-MAP2c binding much less, in agreement with the results of our tubulin co-sedimentation measurements. The specific location of the major MAP2c phosphorylation site in a region homologous to the muscarinic receptor-binding site of Tau suggests that MAP2c also may regulate processes other than microtubule dynamics.Cytoskeletal microtubule-associated proteins (MAPs) 3 are proteins of critical importance for regulating the stability and dynamics of microtubules (1). MAP2 and Tau represent MAP subfamilies expressed in neurons; MAP2 is localized in dendrites, whereas Tau is found mainly in axons (2). Tau and MAP2 belong to the class of intrinsically disordered proteins (IDPs), which lack a unique structure and which exist in multiple, quickly interconverting conformations (3-7). NMR is the method of choice for structural investigation of this type of protein. Tau and MAP2 differ in their N-terminal projection domains, which contain acidic and proline-rich subdomains, whereas the C-terminal parts, containing the microtubulebinding domain (MTBD) and the C-terminal region, are homologous (8). Tau is expressed in several splice variants. The human brain isoforms differ in the number of microtubulebinding regions (MTBRs) in the C-terminal portion and in the presence of two inserts near the N terminus. For the sake of simplicity, only the 441-residue variant lacking exons 6, 8, and 10 (9) is discussed in this paper. This variant has been studied in detail and was shown to form paired helical filaments and neurofibillary tangles in brains of patients suffering from Alzheimer's disease (10). The MAP2 family is composed of two high-molecular-weight proteins, MAP2a and MAP2b, each consisting of 1830 amino acids, and two low-molecular-weight proteins, MAP2c and MAP2d, consisting of 467 and 498 amino acids, respectively. The ...

Mutations of cysteine are often introduced to e.g. avoid formation of non-physiological inter-molecular disulfide bridges in in-vitro experiments, or to maintain specificity in labeling experiments. Alanine or serine is typically preferred, which usually do not alter the overall protein stability, when the original cysteine was surface exposed. However, selecting the optimal mutation for cysteines in the hydrophobic core of the protein is more challenging. In this work, the stability of selected Cys mutants of 14-3-3ζ was predicted by free-energy calculations and the obtained data were compared with experimentally determined stabilities. Both the computational predictions as well as the experimental validation point at a significant destabilization of mutants C94A and C94S. This destabilization could be attributed to the formation of hydrophobic cavities and a polar solvation of a hydrophilic side chain. A L12E, M78K double mutant was further studied in terms of its reduced dimerization propensity. In contrast to naïve expectations, this double mutant did not lead to the formation of strong salt bridges, which was rationalized in terms of a preferred solvation of the ionic species. Again, experiments agreed with the calculations by confirming the monomerization of the double mutants. Overall, the simulation data is in good agreement with experiments and offers additional insight into the stability and dimerization of this important family of regulatory proteins.

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