Protein-chromophore interactions: spectral shifts report the consequences of mutations in the bacterial photosynthetic reaction center

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Vol. 54; no. 9; pp. 1247 - 1267
• Main Authors: DiMagno, T.J, Laible, P.D, Reddy, N.R, Small, G.J, Norris, J.R, Schiffer, M, Hanson, D.K
• Format: Journal Article
• Language: English
• Published: United States Elsevier B.V 15.08.1998
• Subjects: 08 HYDROGEN; ABSORPTION SPECTRA; AMINO ACIDS; ATOMS; Bacteriochlorophyll a; Bacteriopheophytin a; CHARGE DISTRIBUTION; Electron transfer; HYDROGEN; KINETICS; MUTATIONS; PHOTOSYNTHETIC REACTION CENTERS; QUINONES; Site-specific mutagenesis; SPECTRAL SHIFT; STRAINS; Transient absorption spectroscopy; Electron transfer; Bacteriopheophytin a; Site-specific mutagenesis; Transient absorption spectroscopy; Bacteriochlorophyll a
• ISSN: 1386-1425
• DOI: 10.1016/S1386-1425(98)00074-2

Features of the low temperature absorption spectra of reaction centers from a large family of Rhodobacter capsulatus strains carrying site-specific mutations at the M208Tyr and L181Phe positions are presented. Through systematic analysis of the observed electronic transitions (with accompanying vibronic bands), the primary effects of many of the mutations have been identified and explained in terms of the reaction center structure. Some of the observed shifts are comparable to those that have been seen in other systems as a result of formation of hydrogen bonds or hexacoordination of the central Mg atom in bacteriochlorophyll species. Shifts of the Q y and Q x bacteriochlorophyll bands are also seen as a result of distant mutations near the quinones that change the charge distribution of the reaction center. We include kinetic data which show that the spectral and kinetic characteristics of different cofactors can be modulated depending on the particular amino acid that is substituted at the M208 site.