Luogo: Aula Newton, Plesso FisicoRelatore: Prof.ssa Emina A. Stojković - Northeastern Illinois University, ChicagoE-mail organizzatore: raffaella.burioni@unipr.it Abstract:Phytochromes (PHYs) are photoreceptor proteins first discovered in plants,where they control a variety of photomorphogenesis events. PHYs can switchbetween a red light absorbing (Pr) and a far-red absorbing (Pfr) form inresponses to different light qualities, i.e. they are photochromic. Theunexpected discovery of Bacteriophytochromes (BphPs) in non-photosyntheticbacteria, has opened new frontiers in our understanding of the mechanismsby which these natural photoswitches can control single cell development,although the role of BphPs in vivo remains largely unknown. BphPs of thenon-photosynthetic myxobacterium Stigmatella aurantiaca are of specialinterest. Myxobacteria are distinguished among prokaryotes by amulticellular stage in their life cycle known as fruiting bodies, which inStigmatella aurantiaca is controlled by light. The two BphPs from S.aurantiaca, SaBphP1 and SaBphP2, have distinct photochemistry, althoughthey 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 bilin chromophore and undergoes limitedPr/Pfr photoconversion, that can be restored by a single Thr289Hismutation in the bilin-binding domain. Furthermore, the crystal structuresof SaBphP1 wild-type and Thr289His mutant differ in the conformation ofthe chromophore binding cavity. Our structural and sequence analyses of S.aurantiaca’s BphPs highlight critical His289 interactions with thechromophore and suggest the function for BphPs in fruiting myxobacteria.