Title

Characterization of the Carboxysomal Carbonic anhydrase CsoSCA from Halothiobacillus neapolitanus

Document Type

Article

Publication Date

12-1-2006

Department

Chemistry and Biochemistry

Abstract

In cyanobacteria and many chemolithotrophic bacteria, the CO2-fixing enzyme ribullose 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., 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, 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 CO2 that has been produced by CsoSCA through directional dehydration of cytoplasmic bicarbonate. This CO2 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.

Publication Title

Journal of Bacteriology

Volume

188

Issue

23

First Page

8087

Last Page

8094