1 research outputs found
Structural and spectropotentiometric analysis of Blastochloris viridis heterodimer mutant reaction center
Heterodimer mutant reaction centers (RCs) of Blastochloris viridis were crystallized using microfluidic
technology. In this mutant, a leucine residue replaced the histidine residue which had acted as a fifth ligand
to the bacteriochlorophyll (BChl) of the primary electron donor dimer M site (HisM200). With the loss of the
histidine-coordinated Mg, one bacteriochlorophyll of the special pair was converted into a bacteriopheophytin (BPhe), and the primary donor became a heterodimer supermolecule. The crystals had dimensions
400 × 100 ×100 μm, belonged to space group P43212, and were isomorphous to the ones reported earlier for
the wild type (WT) strain. The structure was solved to a 2.5 Å resolution limit. Electron-density maps
confirmed the replacement of the histidine residue and the absence of Mg. Structural changes in the
heterodimer mutant RC relative to the WT included the absence of the water molecule that is typically
positioned between the M side of the primary donor and the accessory BChl, a slight shift in the position of
amino acids surrounding the site of the mutation, and the rotation of the M194 phenylalanine. The
cytochrome subunit was anchored similarly as in the WT and had no detectable changes in its overall
position. The highly conserved tyrosine L162, located between the primary donor and the highest potential
heme C380, revealed only a minor deviation of its hydroxyl group. Concomitantly to modification of the BChl
molecule, the redox potential of the heterodimer primary donor increased relative to that of the WT
organism (772 mV vs. 517 mV). The availability of this heterodimer mutant and its crystal structure provides
opportunities for investigating changes in light-induced electron transfer that reflect differences in redox
cascades