FIGURE 4:

Msps TOG4 is structurally distinct from Msps TOG2. (A) Pairwise alignment of Msps TOG4 (color) and Msps TOG2 (gray) across the full domain yields a 4.5-Å rmsd. (B, C) Pairwise alignment of Msps TOG4 and Msps TOG2 across the first HR triad (B; 2.0 Å rmsd) and the second HR triad (C; 2.8 Å rmsd). (D) Superpositioning of Msps TOG4 and Msps TOG2 based on the first HR triad alignment shown in B, highlighting the 45° difference in the orientation of each domain's second HR triad and the 19-Å differential placement of HR F. (E) Comparative views of Msps TOG4 and Msps TOG2 structures oriented as in D; models shown below. (F) The Msps TOG4 α4B′-α4C′ interface contains bulky, conserved residues, whereas the Msps TOG2 α2B′-α2C′ interface has conserved residues with no or small side chains. (G) Msps TOG4 contains the α4D₁ helical insert that forms an extensive interaction network at the base of HR C and HR D, absent in Msps TOG2.