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Temperature and cryoprotectant influence secondary quinone binding position in bacterial reaction centers
Author(s) -
Pokkuluri P.Raj,
Laible Philip D,
Crawford Adam E,
Mayfield Joy F,
Yousef Mohammed A,
Ginell Stephan L,
Hanson Deborah K,
Schiffer Marianne
Publication year - 2004
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/j.febslet.2004.06.042
Subject(s) - rhodobacter sphaeroides , cryoprotectant , quinone , chemistry , photosynthetic reaction centre , crystallography , ethylene glycol , stereochemistry , electron transfer , photochemistry , photosynthesis , biochemistry , organic chemistry , biology , embryo , cryopreservation , microbiology and biotechnology
We have determined the first de novo position of the secondary quinone Q B in the Rhodobacter sphaeroides reaction center (RC) using phases derived by the single wavelength anomalous dispersion method from crystals with selenomethionine substitution. We found that in frozen RC crystals, Q B occupies primarily the proximal binding site. In contrast, our room temperature structure showed that Q B is largely in the distal position. Both data sets were collected in dark‐adapted conditions. We estimate that the occupancy of the Q B site is 80% with a proximal: distal ratio of 4:1 in frozen RC crystals. We could not separate the effect of freezing from the effect of the cryoprotectants ethylene glycol or glycerol. These results could have far‐reaching implications in structure/function studies of electron transfer in the acceptor quinone complex because the above are the most commonly used cryoprotectants in spectroscopic experiments.