Fig. 4: NMR structure of the C-terminal domain of the human SPAG1 protein and its interactions with PIH1D2.
A Backbone representation of the 20 best NMR structures (α-helices indicated in green) of SPAG1_C. B Cartoon representation of the superimposition of the NMR structures of the C-terminal domain of human SPAG1 (SPAG1_C, green) and RPAP3 (RPAP3_C, blue) proteins. The break in the helix α4, common to SPAG1 and RPAP3 is indicated, as well as the covering loop specific of SPAG1. C Slices extracted from the 1H-15N NOESY-HSQC spectrum recorded on a 2H/13C/15N-labeled PIH1D2_CS:SPAG1622-762 complex. NOE cross-peak linking amide protons belonging to individual spin systems are highlighted using dash blue lines. They reveal a spatial proximity between residues whose label is indicated on the top of the slice (green and orange labels for SPAG1622-762, and PIH1D2’s CS domain (P2_CS), respectively). D Superimposition of the five AF3 predicted models of the PIH1D2_CS:SPAG1622-762 complex structure. In the upper panel, five predicted structures were aligned on the one PIH1D2_CS (orange). The TPR3 domains of five SPAG1 predicted structures were shown in different colors (TPR3_1 to TPR3_5), indicating that relative position of SPAG1 TPR3 with respect to PIH1D2_CS was poorly predicted by AF3. The region of the complex with the highest convergence rate is highlighted in a circle and includes PIH1D2_CS (orange) and SPAG1752-762 region of all five SPAG1622-762 predicted structures. The lower panels shown a zoom in of the high convergence region, highlighting residues at the interface, with dashed lines indicating experimentally observed NOE data from Fig. 4C. The fragment 752-762 of SPAG1 is shown in green, PIH1D2_CS is shown in orange. E Structures of the PIH1D2_CS, PIH1D1_CS, and yeast Pih1_CS bound to SPAG1, RPAP3 and yeast Tah1, respectively. The structures come from AF3 (this work), X-ray (6GXZ.pdb) and NMR (2MNJ.pdb), respectively. The limits of each protein fragment are indicated.
