Martedì 7 Giugno 2016 - Ore 16:30 - Seminario di Dipartimento - Emina A. Stojković - Structural basis for light-control of cell development: new insights from bacterial phytochrome proteins

Luogo:  Aula Newton, Plesso Fisico

Relatore: Prof.ssa Emina A. Stojković - Northeastern Illinois University, Chicago

E-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 switch

between a red light absorbing (Pr) and a far-red absorbing (Pfr) form in

responses to different light qualities, i.e. they are photochromic. 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,

although the role of BphPs in vivo remains largely unknown. BphPs of 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. The two BphPs from S.

aurantiaca, SaBphP1 and SaBphP2, 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 bilin chromophore and undergoes limited

Pr/Pfr photoconversion, that can be restored by a single Thr289His

mutation in the bilin-binding domain. Furthermore, the crystal structures

of SaBphP1 wild-type and Thr289His mutant differ in the conformation of

the chromophore binding cavity. Our structural and sequence analyses of S.

aurantiaca’s  BphPs highlight critical His289 interactions with the

chromophore and suggest the function for BphPs in fruiting myxobacteria.