Myxobacterial fruiting bodies, and the architecture of BphPs. (a) S. aurantiaca fruiting bodies formed on filter paper in starvation media. (b) The architecture of BphPs. The PCM consists of PAS, GAF and PHY, and the CBD consists of PAS and GAF domains. The chromophore binds near the PAS and GAF domains, and is bound to a Cys. ST is the sensory tongue which probes the configuration of the BV chromophore and transmits the signal to the PHY domain. Amino-acid sequence numbers are given for the SaBphP1 (Huntley et al., 2011). (c) The BV chemical structure found in the syn-syn-anti ZZZ configuration in the dark-adapted Pr state. The Z to E isomerization takes place at the double bond marked by the red arrow.