Cleanenergy needs more effective ways of converting sunlight into biofuel. Major advances in this area have occurred in recent years as scientistshave begun to gain insight into the fundamental reactions that drivephotosynthesis. Scientists have focused principally on photosyntheticorganisms like cyanobacteria as promising candidate sources ofbioenergy. One of the limitations to understanding the photosynthesisprocess, which made it difficult to identify proteins associated with acomplex called photosystem II (PSII) because of their relatively shortassociation periods.
Researchers from Pacific Northwest National Laboratoryand Washington University in St. Louis have developed a new approachthat uses a high-sensitivity proteomics approach that allows a morecomprehensive investigation of proteins involved in the complexassembly of PSII. Using this approach, the researchers discovered anovel cluster of genes that encode proteins essential for plants tothrive. They identified six proteins linked to a complex called photosystem II (PSII),which forms a cluster of nine genes—slr0144 to slr0152. The researchersnamed the proteins Pap, for PSII assembly proteins. They identifiedthese components as well as proteins associated with PSII throughoutits life cycle, in functions such as assembly, repair, or degradation.
Photosynthesis is the process by which all green plants andsome algae use sunlight to synthesize organic compounds from carbondioxide and water. One of the initial stages in the chain ofphotosynthesis involves PSII, the membrane protein complex found inorganisms such as green plants, green algae, and cyanobacteria,otherwise known as blue-green algae.
PSII is a light harvesting system that splits water molecules toproduce oxygen. An operon is a cluster of structural genes found inbacteria that are expressed and regulated as a unit. It consists of apromoter and an operator; a promoter is the region of the operon thatacts as an initial binding site during gene transcription. The operatoris a segment of DNA that regulates the activity of the structural genesof the operon, somewhat like an on/off switch.
The researchers used high-throughput proteomics at the U.S. Department of Energy’s Environmental Molecular Sciences Laboratory,a national scientific user facility at PNNL, to study the compositionof isolated PSII complexes. They compared protein profiles from mutantsof a strain of cyanobacterium Synechocystis 6803. To deduce the roleof the Pap operon proteins on cellular function, the researchersperformed a “knockout” of the entire operon. A knockout is a techniquefor deleting or inactivating a gene to determine what role the geneplays by its absence. The researchers observed a measurable decreasein PSII water oxidation caused by a loss of functional PSII complexes,implying a role in stabilizing assembly/degradation events through keybinding interactions.Studies revealing that the cofactor binding sitesof Paps are functional and that they are able to transfercofactors—non-protein compounds required by enzymes to function—couldprovide insight into how they are assembled into the complex. Researchalso will focus on whether Paps are significant to PSII assembly or ifthey help in assembly of other complexes in the electron transportprocess.