DOE JGI Science Highlights: Cyanobacteria shed light on carboxysome complexity

Found in temperate and tropical oceans, Prochlorococcus cyanobacteria are considered the world’s most abundant photosynthetic organisms, able to convert sunlight to energy at depths of 200 meters. Despite their size, they are estimated to contribute up to half of the marine biological carbon sequestration.

Prochlorococcus is a unicellular cyanobacterium that dominates the temperate and tropical oceans. 

(Image courtesy of C.Ting, J.King, S.W.Chisholm, 1999)

The cyanobacteria’s ability to use carbon is attributed in part to the RubisCO enzymes stored in microcompartments known as carboxysomes. Published ahead online December 9, 2011 in the Journal of Bacteriology, DOE JGI Structural Biology head Cheryl Kerfeld and collaborators from the University of California, Berkeley reported the first successful purification and characterization of these carboxysomes. Learning about these containers’ composition and structure, they wrote, can help them understand what advantages the enzymes gain.

Carboxysomes were isolated from a strain of P. marinus and then compared against 29 cyanobacterial genomes for a phylogenetic assay. The team’s findings suggest that the carboxysome’s structure is more complex than had been previously assumed. For example, a double-domain protein unexpectedly turned out to a carboxysome component, playing a role in shell function.

“Our findings have important implications for the structure, function and regulation of α-carboxysomes and suggest that the protein composition of these important bacterial organelles warrants a closer look beyond what was assumed to be a solved problem,” the team concluded.