CRYSTALLOGRAPHIC STUDIES OF MUTANT REACTION CENTERS FROM RHODOBACTER-SPHAEROIDES

X-ray structures have been determined for five mutant reaction centres from Rhodobacter sphaeroides, at resolutions varying between 3.4 Angs trom and 2.3 Angstrom. The aim was to examine the effects of mutagenes is of polar residues in the binding pocket of the reaction centre caro tenoid. The number of water molecules identified in each structure dep ended on the resolution and completeness of the data. In a 2.3 Angstro m structure for a WM115F/FM197R mutant reaction centre, two water mole cules partially filled the cavity that was created when the tryptophan residue was replaced by a less bulky phenylalanine. Structures obtain ed for four reaction centres with mutations of polar residues in the c arotenoid binding pocket failed to show any significant change in the structure of the reaction centre carotenoid. Low resolution data for a YM210W mutant reaction centre showed that the overall structure of th is complex is well conserved. This finding is discussed in light of th e intriguing spectroscopic properties of the YM210W mutant reaction ce ntre, and an alternative pathway for transmembrane electron transfer i dentified in this mutant.