The NDH-1L-PSI Supercomplex Is Important for Efficient Cyclic Electron Transport in Cyanobacteria

Area of Science:

• Photosynthesis research
• Cyanobacterial energy metabolism
• Protein complex assembly

Background:

• Cyclic electron transport (CET) is vital for ATP production in photosynthesis.
• The role of linker proteins in photosystem assembly and function remains an active area of investigation.
• NDH-1 complexes are involved in CET, but their precise interactions with other photosystems are not fully elucidated.

Purpose of the Study:

• To investigate the function of the CpcG2 protein in Synechocystis sp. strain PCC 6803.
• To determine the role of CpcG2 in the NDH-1-dependent cyclic electron transport pathway.
• To identify novel protein complexes involved in photosystem I (PSI) function and light adaptation.

Main Methods:

• Isolation and characterization of high light-sensitive mutants with tags in sll1471 (CpcG2).
• Blue native-PAGE, immunoblotting, mass spectrometry, coimmunoprecipitation, and pull-down assays.
• Analysis of wild-type, mutant strains (cpcG2 deletion, PSI-less, NDH-1 deficient) under varying light conditions.

Main Results:

• Two high light-sensitive mutants were identified with tags in CpcG2, exhibiting impaired NDH-1-dependent CET.
• A novel NDH-1L-CpcG2-PSI supercomplex was detected in wild-type but absent in cpcG2 deletion and PSI-less mutants.
• CpcG2 is essential for the stabilization of the NDH-1L-CpcG2-PSI supercomplex, impacting PSI center number and CET efficiency.

Conclusions:

• CpcG2 acts as a crucial linker protein, forming a stable NDH-1L-CpcG2-PSI supercomplex.
• This supercomplex facilitates efficient NDH-1-dependent cyclic electron transport in cyanobacteria.
• The CpcG2-mediated supercomplex plays a significant role in high light adaptation by optimizing PSI function.