Functional Characterization of the Small Regulatory Subunit PetP from the Cytochrome b₆f Complex in Thermosynechococcus elongatus

Abstract

The cyanobacterial cytochrome b 6 f complex is central for the coordination of photosynthetic and respiratory electron transport and also for the balance between linear and cyclic electron transport. The development of a purification strategy for a highly active dimeric b 6 f complex from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 enabled characterization of the structural and functional role of the small subunit PetP in this complex. Moreover, the efficient transformability of this strain allowed the generation of a DpetP mutant. Analysis on the whole-cell level by growth curves, photosystem II light saturation curves, and P700 + reduction kinetics indicate a strong decrease in the linear electron transport in the mutant strain versus the wild type, while the cyclic electron transport via photosystem I and cytochrome b 6 f is largely unaffected. This reduction in linear electron transport is accompanied by a strongly decreased stability and activity of the isolated DpetP complex in comparison with the dimeric wild-type complex, which binds two PetP subunits. The distinct behavior of linear and cyclic electron transport may suggest the presence of two distinguishable pools of cytochrome b 6 f complexes with different functions that might be correlated with supercomplex formation.

Chloroplast genomes as a tool to resolve red algal phylogenies: a case study in the Nemaliales

“…petP is a subunit of the cytochrome b 6 f complex with no essential role in the overall function of the complex [ 37 ]. It has been identified in cyanobacteria and in bangiophytes but it is apparently absent in green algae and land plants [ 38 ].…”

Cytochrome b6f – Orchestrator of photosynthetic electron transfer

“…These pigments are found associated with subIV but their exact functions remain unclear. PetO [34] and PetP [35] are also present in the Chlamydomonas and cyanobacterial cytb6f complexes, respectively, though to date, they have not been identified in any of the high-resolution structures so far published.…”

Catalytic Reactions and Energy Conservation in the Cytochrome bc1 and b6f Complexes of Energy-Transducing Membranes

“…The analogous Cyt bc 1 consists of eleven subunits in the yeast, PDB ID: 1KYO and bovine, PDB ID: 1QCK, 1BE3 complex, and three in the complex from the photosynthetic bacterium, Rhodobacter sphaeroides . In all cases, the dimeric structure of the complex is required for a physiologically significant electron transfer activity, 250–400 electrons transferred (Cyt f/ sec) −1 . − This is possibly because of a defined intermonomer quinol entry pathway. …”