Structure of the photosynthetic reaction centre from Rhodobacter sphaeroides reconstituted with anthraquinone as primary quinone Q(A)

In the photosynthetic reaction centre (RC) from the purple bacterium Rhodob acter sphaeroides, the primary quinone, a ubiquinone-10 (Q(A)), has been su bstituted by anthraquinone, Three-dimensional crystals have been grown from the modified RC and its structure has been determined by X-ray crystallogr aphy to 2.4 Angstrom resolution, The bindings of the head-group from ubiqui none-10 and of the anthraquinone ring are very similar. In particular, both rings are parallel to each other and the hydrogen bonds connecting the nat ive ubiquinone-10 molecule to AlaM260 and HisM219 are conserved in the anth raquinone containing RC, The space of the phytyl tail missing in the anthra quinone exchanged RC is occupied by the alkyl chain of a detergent molecule , Other structural changes of the Q(A)-binding site are within the limit of resolution. Our structural data bring strong credit to the very large amou nt of spectroscopic data previously achieved in anthraquinone-replaced RCs and which have participated in the determination of the energetics of the q uinone system in bacterial RCs, (C) 2000 Federation of European Biochemical Societies.