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Photosynthetic reaction center; Primary donor; Site-directed mutagenesis; X-ray crystallography; Fourier transform infrared spectroscopy
Abstract:
In bacterial reaction centers the charge separation process across the photosynthetic membrane is predominantly driven by the excited state of the bacteriochlorophyll dimer (D). An X-ray structure analysis of the Phe M197→Tyr mutant reaction center from Rhodobacter sphaeroides at 2.7 Å resolution suggests the formation of a hydrogen bond as postulated by Wachtveitl et al. [Biochemistry 32, 12875–12886, 1993] between the Tyr M197 hydroxy group and one of the 2a-acetyl carbonyls of D. In combination with electrochemically induced FTIR difference spectra showing a split band of the π-conjugated 9-keto carbonyl of D, there is clear evidence for the existence of such a hydrogen bond.
