X-Ray structure determination of three mutants of the bacterial photosynthetic reaction centers from Rb. sphaeroides; altered proton transfer pathways.
In the photosynthetic reaction center (RC) from Rhodobacter sphaeroides, the reduction of a bound quinone molecule Q(B) is coupled with proton uptake. When Asp-L213 is replaced by Asn, proton transfer is inhibited. Proton transfer was restored by two second-site revertant mutations, Arg-M233-->Cys and Arg-H177-->His. Kinetic effects of Cd(2+) on proton transfer showed that the entry point in revertant RCs to be the same as in the native RC. The structures of the parental and two revertant RCs were determined at resolutions of 2.10, 1.80, and 2.75 A. From the structures, we were able to delineate alternate proton transfer pathways in the revertants. The main changes occur near Glu-H173, which allow it to substitute for the missing Asp-L213. The electrostatic changes near Glu-H173 cause it to be a good proton donor and acceptor, and the structural changes create a cavity which accommodates water molecules that connect Glu-H173 to other proton transfer components.
Xu
Qiang
Q
Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA.
Axelrod
Herbert L
HL
Abresch
Edward C
EC
Paddock
Mark L
ML
Okamura
Melvin Y
MY
Feher
George
G
D001665:Binding Sites; D002104:Cadmium / Q000378:metabolism; D018360:Crystallography, X-Ray; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011522:Protons; D012242:Rhodobacter sphaeroides / Q000737:chemistry / Q000378:metabolism
D045322:Photosynthetic Reaction Center Complex Proteins; D011522:Protons; D002104:Cadmium