4ht5
CO2 concentrating mechanism protein P, CcmP form 1CO2 concentrating mechanism protein P, CcmP form 1
Structural highlights
FunctionCCMP_SYNE7 Probably part of the carboxysome shell, a polyhedral inclusion where RuBisCO (ribulose bisphosphate carboxylase, rbcL-rbcS) is sequestered. It is thought that this protein controls transport of RuBisCO reactants in and out of the carboxysome; residual densities in the 4 X-ray structures suggest that differing compounds bind in interior pockets, depending on the open or closed state of the pore.[1] Publication Abstract from PubMedThe carboxysome is a bacterial organelle found in all cyanobacteria; it encapsulates CO2 fixation enzymes within a protein shell. The most abundant carboxysome shell protein contains a single bacterial microcompartment (BMC) domain. We present in vivo evidence that a hypothetical protein (dubbed CcmP) encoded in all beta-cyanobacterial genomes is part of the carboxysome. We show that CcmP is a tandem BMC domain protein, the first to be structurally characterized from a beta-carboxysome. CcmP forms a dimer of tightly stacked trimers, resulting in a nanocompartment-containing shell protein that may weakly bind 3-phosphoglycerate, the product of CO2 fixation. The trimers have a large central pore through which metabolites presumably pass into the carboxysome. Conserved residues surrounding the pore have alternate side-chain conformations suggesting that it can be open or closed. Furthermore, CcmP and its orthologs in alpha-cyanobacterial genomes form a distinct clade of shell proteins. Members of this subgroup are also found in numerous heterotrophic BMC-associated gene clusters encoding functionally diverse bacterial organelles, suggesting that the potential to form a nanocompartment within a microcompartment shell is widespread. Given that carboxysomes and architecturally related bacterial organelles are the subject of intense interest for applications in synthetic biology/metabolic engineering, our results describe a new type of building block with which to functionalize BMC shells. The structure of CcmP, a tandem bacterial microcompartment domain protein from the beta-carboxysome, forms a subcompartment within a microcompartment.,Cai F, Sutter M, Cameron JC, Stanley DN, Kinney JN, Kerfeld CA J Biol Chem. 2013 May 31;288(22):16055-63. doi: 10.1074/jbc.M113.456897. Epub, 2013 Apr 9. PMID:23572529[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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