The SFB 1078 kindly invites you to the the following colloquium talk, hosted by Maria-Andrea Mroginski.

Prof. Emina Stojkovic (Northeastern Illinois University, Chicago, USA)

Title: Structural Basis for Light Control of Cell Development: New Insights from Bacterial Phytochrome Proteins

Abstract: Phytochromes (PHYs) are photoreceptor proteins first discovered in plants, where they control a variety of photomorphogenesis events. PHYs as photochromic enzymes that usually contain c-terminal kinase domain can reversibly switch between a red light absorbing (Pr) and a far-red light absorbing (Pfr) state. The unexpected discovery of bacteriophytochromes (BphPs) in non-photosynthetic bacteria has opened new frontiers in our understanding of the mechanisms by which these natural photoswitches can control single cell development. BphPs from the non-photosynthetic myxobacterium Stigmatella aurantiaca are of special interest. Myxobacteria are distinguished among prokaryotes by a multicellular stage in their life cycle known as fruiting bodies, which in Stigmatella aurantiaca is controlled by light. We recently determined the crystal structures of the two BphPs from S. aurantiaca, denoted SaBphP1 and SaBphP2. They have distinct photochemistry, although they bind the same bilin chromophore and share a large sequence identity. Unlike classical BphPs, wild-type SaBphP1 lacks a conserved histidine (His289) that stabilizes the covalently-bound bilin chromophore and undergoes limited Pr/Pfr photoconversion that can be restored by a single Thr289His mutation. Furthermore, the crystal structures of SaBphP1 wild-type and Thr289His mutant in comparison to classical SaBphP2 wild-type protein differ in the conformation of the essential bilin chromophore as well as important protein dimer interface in the dark-adapted Pr state. Our structural and sequence analyses of S. aurantiaca’s BphPs highlight critical amino acid interactions with the chromophore and suggest the function for BphPs in the fruiting myxobacteria.