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.
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http://dx.doi.org/10.1042/BCJ20160773 | DOI Listing |
Front Immunol
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First Department of Pediatrics, Weifang People's Hospital Affiliated to Shandong Second Medical University, Weifang, China.
Autoimmune cerebellar ataxia (ACA) is a cerebellar syndrome induced by autoimmune reactions and its onset is induced by malignant tumors, prodromic infection, and gluten allergy. Its clinical symptoms include gait disorder, limb ataxia, dysarthria, and dysphagia. According to , the diagnosis of ACA is based on the following points: 1.
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May 2025
Bioscience and Biomedical Engineering Thrust, The Hong Kong University of Science and Technology (Guangzhou), Guangzhou, 511400, China.
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View Article and Find Full Text PDFJ Sci Food Agric
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Bee and Natural Products R&D and P&D Application and Research Center, Bingöl University, Bingöl, Turkey.
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Laboratory of Ecophysiology and Molecular Evolution, National Institute for Amazonian Research, Manaus, Brazil.
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View Article and Find Full Text PDFJ Phys Chem B
January 2025
School of Chemistry, The University of New South Wales, Sydney, NSW 2052, Australia.
A systematic series of QM cluster models has been developed to predict the trend in the carbonic anhydrase binding affinity of a structurally diverse dataset of ligands. Reference DLPNO-CCSD(T)/CBS binding energies were generated for a cluster model and used to evaluate the performance of contemporary density functional theory methods, including Grimme's "3c" DFT composite methods (rSCAN-3c and ωB97X-3c). It is demonstrated that when validated QM methods are used, the predictive power of the cluster models improves systematically with the size of the cluster models.
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