Cyanobacterial carboxysomes: microcompartments that facilitate CO2 fixation.
Carboxysomes are extraordinarily efficient proteinaceous microcompartments that encapsulate the primary CO2-fixing enzyme (ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBisCO) in cyanobacteria and some proteobacteria. These microbodies form part of a CO2-concentrating mechanism (CCM), operating together with active CO2 and HCO3(-) uptake transporters which accumulate HCO3(-) in the cytoplasm of the cell. Cyanobacteria (also known as blue-green algae) are highly productive on a global scale, especially those species from open-ocean niches, which collectively contribute nearly 30% of global net primary fixation. This productivity would not be possible without a CCM which is dependent on carboxysomes. Two evolutionarily distinct forms of carboxysome are evident that encapsulate proteobacterial RuBisCO form-1A or higher-plant RuBisCO form- 1B, respectively. Based partly on RuBisCO phylogeny, the two carboxysome types are known either as α-carboxysomes, found in predominantly oceanic cyanobacteria (α-cyanobacteria) and some proteobacteria, or as β-carboxysomes, found mainly in freshwater/estuarine cyanobacteria (β-cyanobacteria). Both carboxysome types are believed to have evolved in parallel as a consequence of fluctuating atmospheric CO2 levels and evolutionary pressure acting via the poor enzymatic kinetics of RuBisCO. The three-dimensional structures and protein components of each carboxysome type reflect distinct evolutionarily strategies to the same major functions: subcellular compartmentalization and RuBisCO encapsulation, oxygen exclusion, and CO2 concentration and fixation.
Division of Plant Science, The Australian National University, Canberra, A.C.T., Australia.
Benjamin D
BD
Rae
Benedict M
BM
Long
Lynne F
LF
Whitehead
Britta
B
Förster
Murray R
MR
Badger
G Dean
GD
Price
D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism*; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D046911:Macromolecular Substances / Q000378:metabolism*; D015388:Organelles / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D014871:Water Microbiology
D046911:Macromolecular Substances; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase