title: The structure of CcmP, a tandem bacterial microcompartment domain protein from the β-carboxysome, forms a subcompartment within a microcompartment.
abstract: The 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 β-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 β-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 α-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.
authors.affiliation: United States Department of Energy-Joint Genome Institute, Walnut Creek, California 94598, USA.
authors.forename: Fei
authors.initials: F
authors.lastname: Cai
authors.forename: Markus
authors.initials: M
authors.lastname: Sutter
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Cameron
authors.forename: Desiree N
authors.initials: DN
authors.lastname: Stanley
authors.forename: James N
authors.initials: JN
authors.lastname: Kinney
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Kerfeld
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016680:Genome, Bacterial / Q000502:physiology; D005988:Glyceric Acids / Q000737:chemistry / Q000378:metabolism; D005810:Multigene Family / Q000502:physiology; D055503:Protein Multimerization / Q000502:physiology*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D046940:Synechococcus / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D005988:Glyceric Acids; C005156:3-phosphoglycerate
keywords: CO2 Fixation; Carbon Dioxide; Carboxysome; Cell Compartmentation; Microbiology; Microcompartment; Protein Self-assembly; Protein Structure