5SWC

The structure of the beta-carbonic anhydrase CcaA

Summary for 5SWC

• Entry DOI: 10.2210/pdb5swc/pdb
• Descriptor: Carbonic anhydrase, ZINC ION, CHLORIDE ION, ... (5 entities in total)
• Functional Keywords: carboxysome, bacterial microcompartment, carbonic anhydrase, symmetry breaking, carbon fixation, lyase
• Biological source: Synechocystis sp. (strain PCC 6803 / Kazusa)
• Total number of polymer chains: 6
• Total formula weight: 162764.61

Authors

Kimber, M.S.,McGurn, L.,White, S.A. (deposition date: 2016-08-08, release date: 2016-10-26, Last modification date: 2023-10-04)

Primary citation

McGurn, L.D.,Moazami-Goudarzi, M.,White, S.A.,Suwal, T.,Brar, B.,Tang, J.Q.,Espie, G.S.,Kimber, M.S.
The structure, kinetics and interactions of the beta-carboxysomal beta-carbonic anhydrase, CcaA.
Biochem. J., 473:4559-4572, 2016

PubMed Abstract: CcaA is a β-carbonic anhydrase (CA) that is a component of the carboxysomes of a subset of β-cyanobacteria. This protein, which has a characteristic C-terminal extension of unknown function, is recruited to the carboxysome via interactions with CcmM, which is itself a γ-CA homolog with enzymatic activity in many, but not all cyanobacteria. We have determined the structure of CcaA from Synechocystis sp. PCC 6803 at 1.45 Å. In contrast with the dimer-of-dimers organization of most bacterial β-CAs, or the loose dimer-of-dimers-of-dimers organization found in the plant enzymes, CcaA shows a well-packed trimer-of-dimers organization. The proximal part of the characteristic C-terminal extension is ordered by binding at a site that passes through the two-fold symmetry axis shared with an adjacent dimer; as a result, only one of a pair of converging termini can be ordered at any given time. Docking in Rosetta failed to find well-packed solutions, indicating that formation of the CcaA/CcmM complex probably requires significant backbone movements in at least one of the binding partners. Surface plasmon resonance experiments showed that CcaA forms a complex with CcmM with sub-picomolar affinity, with contributions from residues in CcmM's αA helix and CcaA's C-terminal tail. Catalytic characterization showed CcaA to be among the least active β-CAs characterized to date, with activity comparable with the γ-CA, CcmM, it either complements or replaces. Intriguingly, the C-terminal tail appears to partly inhibit activity, possibly indicating a role in minimizing the activity of unencapsulated enzyme.

PubMed: 27729545
DOI: 10.1042/BCJ20160773

Experimental method

X-RAY DIFFRACTION (1.45 Å)