The MPS1 kinase NTE region has helical propensity and preferred conformations towards the TPR domain

Abstract

The mitotic spindle assembly checkpoint (SAC) ensures accurate segregation of chromosomes by preventing onset of anaphase until all chromosomes are properly attached to spindle microtubules. The Monopolar spindle 1 (MPS1) kinase is one of the SAC components, localizing at unattached kinetochores by an N-terminal localization module. This module comprises a flexible NTE module and the TPR domain, which we previously characterized for their contribution to kinetochore binding. Here we discuss the conformations of the highly flexible NTE with respect to the TPR domain, using paramagnetic NMR. The distance restraints derived from paramagnetic relaxation enhancements (PREs) show that the mobile NTE can be found in proximity of a large but specific part of the surface area of the TPR domain. To sample the conformational space of the NTE in the context of the NTE-TPR module, we used the ab initio Rosetta approach supplemented by paramagnetic NMR restraints. We find that many NTE residues have a propensity to form helical structures and that the module localizes at the convex surface of the TPR domain. This work demonstrates the highly dynamic nature of the interactions between the NTE and TPR domains and it shows that the convex rather than the canonical concave TPR surface mediates interactions, leading to the auto-inhibition that the TPR exerts upon the NTE region in the context of SAC signaling.