FIG 7.

Graphical representation of the changes in A/B orientation upon bile binding. For these measurements, the apo (EM structure presented here; X-ray structure presented in reference 10) and bile-bound (EM structure presented in reference 24; X-ray structure presented in reference 21) P domain structures were aligned using residues 500 to 530 of the P1 domain core of the A subunit (comparing EM and X-ray structures separately). The EM A and X-ray A lines show the CA distances of the aligned A subunit P1 domains and demonstrate that bile binding does not change the structure of the P1 domain itself. The EM B and X-ray B lines show that if the A subunit P1 domains are aligned, the relative position of the B subunit P1 domain moves by >4 Å in places upon the binding of bile. Therefore, this rotation is observed in both the EM and X-ray structures.