Figure 4. The BBSome BBS7 interacts with conserved SMO helix 8.

(A) Capture assays of BBS7 with mutants of SMO^H8 (aa 543–559) identify Trp549 and Trp553 as the major BBS7-binding determinants of SMO^H8. The sequences of the peptides fused to GST after the protease cleavage site are indicated. (B) Overlay of helix 8 from three structures of human SMO (PDB IDs: 5L7D, 6O3C, 6D32), showing that the orientation of the two tryptophan residues into the hydrophobic core of the membrane is conserved (see additional structures in Figure 3—figure supplement 1D). For consistency with the GST fusions used in capture assays, residue numbering corresponds to mouse SMO. (C) Sequence analysis finds a BBSome-binding motif ([W/F/Y]R) within helix 8 in 20 of the 26 GPCRs known to localize to cilia. Sequences are listed in Supplementary file 3.