Dimerization of core complexes as an efficient strategy for energy trapping in Rhodobacter sphaeroides

Area of Science:

• Bacteriology
• Photosynthesis research
• Biophysics

Background:

• Purple phototrophic bacteria like Rhodobacter sphaeroides utilize light-harvesting LH2 complexes to transfer energy to core complexes.
• Core complexes are typically dimeric in R. sphaeroides, but monomeric forms exist in other species, with the necessity of dimerization not fully understood.

Purpose of the Study:

• To investigate the role of core complex dimerization in photosynthetic energy transfer in R. sphaeroides.
• To compare the light-harvesting and energy trapping properties of native dimeric core complexes with engineered monomeric core complexes.

Main Methods:

• Analysis of Rhodobacter sphaeroides strains with native dimeric or PufX-mutated monomeric core complexes.
• Purification of photosynthetic membranes with varying LH2 complex levels.
• Spectroscopic techniques including absorption, steady-state fluorescence, and picosecond time-resolved fluorescence kinetics.

Main Results:

• Photosynthetic membranes with monomeric core complexes exhibited fluorescence lifetimes nearly twice as long as those with dimeric core complexes under saturating light.
• This increased fluorescence lifetime, indicative of less efficient energy trapping, was consistent across different LH2 levels and with open reaction centers (RCs).

Conclusions:

• Dimeric RC-LH1-PufX core complexes, in conjunction with LH2 complexes, facilitate more efficient energy trapping in Rhodobacter sphaeroides photosynthetic membranes.
• The dimeric state of the core complex is crucial for optimal light-harvesting and energy transfer processes.