FTIR Characterization of Leu M160→His, Leu L131→His and His L168→Phe Mutations Near the Primary Electron Donor in RB. Sphaeroides Reaction Centers

Abstract

Light-induced FTIR difference spectroscopy has been used to monitor structural changes in Rb. sphaeroides mutant reaction centers (RCs) associated with the substitution of amino acids near the primary electron donor (P). In the wild type Rb. sphaeroides RC, the 9keto carbonyls for both BChls constituting P (P_L and P_M) have no specific interactions with the protein. A hydrogen bond probably exists between the 2a acetyl C=O of P_L and His L168^1,2 but no such bond is possible with the symmetry related amino acid on the M side, a Phe residue (M197). The mutations Leu L131→His and Leu M160→His³ (see also Williams et al., these proceedings) were designed to introduce a proton donating residue that could form a hydrogen bond with the keto C=O of ring V of each BChl of the dimer. In addition, the mutation His L168→Phe was designed to break a hydrogen bond between the 2a C=O of P_L and His L168.