Influence of M subunit Thr222 and Trp252 on quinone binding and electron transfer in Rhodobacter sphaeroides reaction centres.
M subunit Trp252 is the only amino acid residue which is located between the bacteriopheophytin HA and the quinone QA in the photosynthetic reaction centre of Rhodobacter sphaeroides. Oligodeoxynucleotide-directed mutagenesis was employed to elucidate the influence of this aromatic amino acid on the electron transfer between these two chromophores. For this, M subunit Trp252 was changed to tyrosine or phenylalanine, and Thr222, which presumably forms a hydrogen bridge to the indole ring of M subunit Trp252, to valine. In all three mutated reaction centres, the electron-accepting ubiquinone QA is less firmly bound to its binding site than in the wild-type protein. The electron transfer from the reduced bacteriopheophytin HA- to QA proceeds in the wild-type and in the mutant ThrM222Val within 220 ps. However, in the mutants TrpM252Tyr and TrpM252Phe the time constants are 600 ps and 900 ps, respectively. This indicates that M subunit Trp252 participates in the binding of QA and reduction of this quinone.
Max-Planck-Institut für Biochemie, Abteilung Membranbiochemie, Martinsried, Germany.
H U
HU
Stilz
U
U
Finkele
W
W
Holzapfel
C
C
Lauterwasser
W
W
Zinth
D
D
Oesterhelt
D001483:Base Sequence; D001665:Binding Sites; D004579:Electron Transport; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D011809:Quinones / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000235:genetics / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism*
D009838:Oligodeoxyribonucleotides; D045322:Photosynthetic Reaction Center Complex Proteins; D011809:Quinones; D013912:Threonine; D014364:Tryptophan