Photoreceptor proteins from purple bacteria

Purple bacteria contain representatives of four of the six main families of photoreceptor proteins: phytochromes, BLUF domain containing proteins, xanthopsins (i.e., photoactive yellow proteins), and phototropins (containing one or more light, oxygen, or voltage (LOV) domains). Most of them have a function in adjusting the cellular transcript profile to the ambient light climate. Here we will discuss, with examples of the most important representative(s) of each of these four families, the interdependent topics: (i) the proteins’ biological functions and their molecular context, (ii) the results of ultra-fast and static spectroscopic studies, and (iii) structural alterations required for initiation of signal transfer, as resolved with transient spectroscopy and the methodology of structural biology.
For all four of these photoreceptor protein families, detailed insight is available about the structural basis of signal generation in the light-input domain. The next main challenge is to understand how this information is transmitted to the downstream partner in the signal transduction chain. This determination will generally require more detailed insight into the spatial arrangement of multi-domain proteins.