Comparisons of the SaBphP1 CBD (a) and PCM (b) in the wild-type and T289H mutant forms. The PAS, GAF and PHY domains are colored yellow, green and magenta, respectively. (a) Overlay of the wild-type CBD (yellow, green) on the T289H mutant CBD (light blue). The CBD is a dimer (marked A and B) which is generated from the monomer in the asymmetric unit by a crystallographic symmetry operation. Thr289 is marked in subunit A, and His289 in subunit B. The circular arrow denotes the six-helix bundle (helices numbered one to six in red, residue numbers are marked) that forms the dimer interface (gray dotted line). The four interacting helices are highlighted by cylinders, which are also displayed in isolation above the structure. The dimer is rotated so that helices four and six of subunit B lay on top of helices one and three of subunit A. The offset angle φ between the subunits is measured as described in Appendix B3. (b) Overlay of the wild-type PCM (yellow, green, magenta) on the T289H mutant PCM (light blue). The four helices at the dimer interface are displayed for both constructs below the structure. The angle between the interfaces φ increases by 14° compared with the CBD. The knot, the kink at the helical transition from GAF to PHY and the sensory tongue are marked. (c) Domain organization of BphPs. Sequence numbers are provided for SaBphP1.