FIGURE 1.
Identification of a TPR motif in the N-terminal region of Mps1. A, amino acid sequence alignment of human N-terminal Mps1 and BUB1 and BUBR1 from different species. Secondary structure elements are mapped onto the crystal structure of N-terminal BUBR1 (Protein Data Bank code 2WVI). Figure was generated with ESPript (68). B, structure model of N-terminal Mps1 predicts this region is organized as a triple tandem of the TPR motif. C, model highlighting the Mps1 residues that are conserved and located in positions that define a canonical TPR motif. Most of these conserved residues are predicted to be engaged in stabilizing stacking interactions. Purple indicates the phosphorylation site serine 80 is highlighted. D, far-UV CD confirms N-terminal Mps1 is organized as a predominantly α-helical region. Inset, the thermal denaturation of this domain is highly cooperative and follows a two-state unfolding process. E, size-exclusion chromatogram of molecular mass markers only (●): peak 1, bovine serum albumin; peak 2, ovalbumin; peak 3, chymotrypsinogen A; peak 4, ribonuclease A. For the second chromatogram (−), the same molecular mass markers were combined with Mps1(1–239) prior to gel filtration. Mps1(1–239) retention time was closed to that of ovalbumin (43 kDa) thus revealing the former self-associates to form stable dimers.