title: Characterization of the carboxysomal carbonic anhydrase CsoSCA from Halothiobacillus neapolitanus.
abstract: In cyanobacteria and many chemolithotrophic bacteria, the CO(2)-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) is sequestered into polyhedral protein bodies called carboxysomes. The carboxysome is believed to function as a microcompartment that enhances the catalytic efficacy of RubisCO by providing the enzyme with its substrate, CO(2), through the action of the shell protein CsoSCA, which is a novel carbonic anhydrase. In the work reported here, the biochemical properties of purified, recombinant CsoSCA were studied, and the catalytic characteristics of the carbonic anhydrase for the CO(2) hydration and bicarbonate dehydration reactions were compared with those of intact and ruptured carboxysomes. The low apparent catalytic rates measured for CsoSCA in intact carboxysomes suggest that the protein shell acts as a barrier for the CO(2) that has been produced by CsoSCA through directional dehydration of cytoplasmic bicarbonate. This CO(2) trap provides the sequestered RubisCO with ample substrate for efficient fixation and constitutes a means by which microcompartmentalization enhances the catalytic efficiency of this enzyme.
authors.affiliation: Department of Chemistry and Biochemistry, The University of Southern Mississippi, Hattiesburg, MS 39406-0001, USA.
authors.forename: Sabine
authors.initials: S
authors.lastname: Heinhorst
authors.forename: Eric B
authors.initials: EB
authors.lastname: Williams
authors.forename: Fei
authors.initials: F
authors.lastname: Cai
authors.forename: C Daniel
authors.initials: CD
authors.lastname: Murin
authors.forename: Jessup M
authors.initials: JM
authors.lastname: Shively
authors.forename: Gordon C
authors.initials: GC
authors.lastname: Cannon
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000378:metabolism*; D002451:Cell Compartmentation / Q000502:physiology; D044222:Halothiobacillus / Q000201:enzymology* / Q000502:physiology; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D011994:Recombinant Proteins; D002245:Carbon Dioxide; D002256:Carbonic Anhydrases