(a) Location of BBS1, BBS2, BBS7, and BBS9 in the BBSome, colored except for their β-propeller domains. GAE heterodimers shown in panels c and d are boxed. In the rotated view all non-colored subunits are removed for clarity. (b) Heterodimerization of BBS2 and BBS7 involves the hx-GAE module. (c) Heterodimerization of BBS1 and BBS9. (d) Superposition of BBS9GAE with the GAE domain of AP-1 clathrin adaptor subunit γ-like 2 reveals that the heterodimerization interface with BBS1GAE would occlude the substrate binding pocket. (e) The GAE-pf module of BBS2, BBS7 and BBS9 resembles the equivalent module of the AP-2 clathrin adaptor α2-adaptin. While BBS9GAE-pf superposes closely with α2-adaptin, the GAE and pf domains of BBS2 and BBS7 (inset) adopt different orientations relative to one another.