Carboxysome Shell Carbonic Anhydrase is a bacterial carbonic anhydrase localised in the carboxysome, where it converts bicarbonate ions to carbon dioxide for use in carbon fixation. It contains three domains, these being: (1) an N-terminal domain composed primarily of four alpha-helices; (2) a catalytic domain containing a tightly bound zinc ion and (3) a C-terminal domain with weak structural similarity to the catalytic domain [1]. This entry represents the C-terminal domain which consists of a central five-stranded mixed beta-sheet with two helices flanking one side of the sheet and one helix flanking the other side and lacks all the necessary zinc ligand residues [1].

1: The structure of beta-carbonic anhydrase from the carboxysomal shell reveals a distinct subclass with one active site for the price of two. Sawaya MR, Cannon GC, Heinhorst S, Tanaka S, Williams EB, Yeates TO, Kerfeld CA; J Biol Chem. 2006;281:7546-7555. PMID:16407248