Microtubule Associated Proteins (MAP) play a key role in regulation of microtubule (MT) dynamics. Products of two genes, MAPT and MAP2, are expressed in nerve cells in multiple isoforms generated by alternative splicing. The former gene encodes protein Tau, which is associated with neurodegenerative processes accompanying the Alzheimer's disease, and has therefore attracted great attention in the past few decades. Microtubule associated protein 2c (MAP2c), the shortest, 467-residue, 49 kDa isoform of the latter gene, is involved in neuronal development and is less characterized than its homologue Tau.
MAP2c consists of several structural and functional regions. The N-terminal domain contains two important parts: The N-terminal region with a high content of negatively charged amino acids and the proline-rich region. The former segment contains a proposed binding site for steroids, while the latter one interacts with SH3 domain of plectin [1] which act as a cytolinker and regulates actin dynamics. The second important part of MAP2c is a highly-conserved C-terminal domain that binds to MTs. Our goal was to characterize the MAP2c interactions, make a comparison to Tau, and deduce the functional differences between MAP2c and Tau.
Identification of structural motifs responsible for specific functions of MAP2c and Tau is complicated by the fact that MAP2c and Tau belong to the class of intrinsically disordered proteins (IDPs) lacking a unique structure and exist in multiple, quickly interconverting conformations. Given the disordered nature of IDPs, NMR is a key experimental method for studying IDPs. We used high-resolution NMR techniques and small angle X-ray scattering to acquire atomic-resolution data reflecting structural and dynamic features of MAP2c [2]. The results allowed us to correlate structural features and dynamics of MAP2c with its known and proposed binding and phosphorylation sites, and to directly compare MAP2c with Tau.
We obtained a detailed description of the transient secondary and tertiary structure of MAP2c. We also identified intramolecular contacts, caused by electrostatic interactions, with a great impact on dynamics of MAP2c. And most importantly, we revealed differences in phosphorylation of Tau and MAP2c, with important consequences for interactions of these proteins.
This work was supported by the program VES17 INTER-EXCELLENCE, subprogram INTER-COST.