Figure 7

Summary of conserved interactions in 'typical' WD-repeats responsible for maintaining the structural integrity of propeller blades 1-5 in RACK1. Interactions are illustrated for blade 2 of the A. thaliana RACK1A structure (PDB: 3DM0). The second WD-repeat (as defined in Figure 6) is shown in its entirety (orange ribbon) and contributes β-strand D to blade 1 plus strands A, B and C of blade 2, terminating in the WD signature residues (W90-D91). Strand D of blade 2 is provided by residues in the third WD repeat (yellow ribbon). A highly conserved Asp residue (D84) occupies the central position of the B-C turn and is networked by hydrogen bonds to residues in the P-2 and P+2 positions (S82 side chain, E86 backbone) as well as through a salt bridge to the signature GH His (H62) in the D-A loop between blades 1 and 2. H62 is further networked with a hydrogen bond to S80 on β-strand B and a hydrogen bond between S80 and W90 (β-strand C). Important non-polar interactions regulate blade packing such as contact between W90 and residues on the reverse face of blade 1 (L59) and between V66 (β-strand A) and the reverse face of the B-C hairpin of blade 1 (not shown). B-C hairpin positions relative to the consensus Asp (P0) are marked in blue.