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. 2020 Jun 8;9:e55954. doi: 10.7554/eLife.55954

Figure 2. Overall structure of the BBSome–ARL6GTP complex.

(A) Two views of the cryo-EM map (transparent surface) and the near-atomic model of the BBSome–ARL6GTP complex shown in ribbon representation. BBS2βprop and BBS7βprop were swapped in our previously published structure, as were BBS2cc and BBS7cc. BBS1βprop, the domain that contacts ARL6GTP, is also labeled. (B) Overall view (left panel) of the BBSome–ARL6GTP complex. Right panel: close-up view focusing on the interaction of the backside of ARL6GTP with the loop connecting BBS7cc and BBS7βprop, and with BBS1βprop. Bottom panel: The Switch 1 and Switch 2 regions change conformation between ARL6GDP for ARL6GTP and these regions are colored orange (ARL6GTP) or red (ARL6GDP). ARL6GTP contacts the BBS1 β-propeller with its Switch 2 region. In contrast, ARL6 contacts BBS7 using a surface that is largely unaffected by nucleotide binding. A homology model of bovine GDP-bound ARL6GTP (based on the crystal structure of the Chlamydomonas protein; PDB ID: 4V0K) was aligned to the model of the GTP-bound ARL6 in our BBSome–ARL6GTP complex (ARL6GDP in light blue and ARL6GTP in lime green). GTP is shown in stick representation.

Figure 2.

Figure 2—figure supplement 1. Cryo-EM analysis of the BBSome–ARL6GTP complex.

Figure 2—figure supplement 1.

(A) Typical cryo-EM image of vitrified BBSome–ARL6GTP complex. Some particles are circled. Scale bar: 50 nm. (B) Selected 2D-class averages obtained with RELION 3.0. Side length of individual averages: 45 nm. (C) Image-processing workflow for 3D classifications and refinement in RELION 3.0 that yielded the three density maps discussed in the main text. See Methods for details.