Light-driven quinone reduction in heliobacterial membranes.

Area of Science:

• Biochemistry
• Photosynthesis research
• Evolutionary biology

Background:

• Photosynthetic reaction centers (RCs) diverged into Type I and Type II, with distinct electron acceptors.
• Photosystem I (PSI) uses menaquinones, but HbRCs' quinone usage remained unclear.
• HbRC crystal structure lacks quinones in analogous PSI sites.

Purpose of the Study:

• To investigate the quinone reduction capability of heliobacterial reaction centers (HbRCs).
• To determine if HbRCs function similarly to Type II RCs under specific conditions.
• To explore the evolutionary relationship between HbRCs, PSI, and Type II RCs.

Main Methods:

• Illumination of heliobacterial membranes to observe menaquinone reduction.
• Experiments on isolated membranes and live heliobacterial cells.
• Spectroscopic analysis of electron transfer pathways.

Main Results:

• Heliobacterial membranes showed menaquinone reduction to menaquinol upon illumination.
• HbRCs appear to switch electron acceptors based on light intensity.
• Preferential reduction of soluble acceptors in low light and quinones in high light.

Conclusions:

• HbRCs can reduce quinones, challenging previous assumptions.
• HbRCs may act as a functional intermediate between PSI and Type II RCs.
• Light-dependent acceptor switching in HbRCs offers insights into RC evolution.