Interconversion of inactive to active conformation of MARK2: Insights from molecular modeling and molecular dynamics simulation.

The Ser/Thr protein kinase MARK2, also known as Par1b, belongs to the highly-conserved family of PAR proteins which regulate cell polarity and partitioning through the animal kingdom. In the current study, inactive and active structures of human MARK2 were constructed by modeling and molecular dynamics simulation, based on available incomplete crystal structures in Protein Data Bank, to investigate local structural changes through which MARK2 switches from inactive to active state. None of the MARK2 wild type inactive crystal structures represent the position of activation segment. So, the contribution of this loop to the formation of inactive state is not clear. In the modeled structure of inactive MARK2, activation segment occludes the enzyme active site and assumes a relatively stable position. We also presented a detailed description of the major structural changes occur through the activation process and proposed a framework on how these deviations might be affected by the phosphorylation of Thr208 or existence of the UBA domain. Inspection of protein active state in the presence of Mg-ATP, demonstrated the precise arrangement of the various parts of enzyme around Mg-ATP and the importance of their stability in localization of the resulting complex. The results also confirmed the alleged mild auto-inhibitory role of the UBA domain and suggested a reason for the necessity of this role, based on structural similarities to other related kinases.