title: Assembly of robust bacterial microcompartment shells using building blocks from an organelle of unknown function.
abstract: Bacterial microcompartments (BMCs) sequester enzymes from the cytoplasmic environment by encapsulation inside a selectively permeable protein shell. Bioinformatic analyses indicate that many bacteria encode BMC clusters of unknown function and with diverse combinations of shell proteins. The genome of the halophilic myxobacterium Haliangium ochraceum encodes one of the most atypical sets of shell proteins in terms of composition and primary structure. We found that microcompartment shells could be purified in high yield when all seven H. ochraceum BMC shell genes were expressed from a synthetic operon in Escherichia coli. These shells differ substantially from previously isolated shell systems in that they are considerably smaller and more homogeneous, with measured diameters of 39±2nm. The size and nearly uniform geometry allowed the development of a structural model for the shells composed of 260 hexagonal units and 13 hexagons per icosahedral face. We found that new proteins could be recruited to the shells by fusion to a predicted targeting peptide sequence, setting the stage for the use of these remarkably homogeneous shells for applications such as three-dimensional scaffolding and the construction of synthetic BMCs. Our results demonstrate the value of selecting from the diversity of BMC shell building blocks found in genomic sequence data for the construction of novel compartments.
authors.affiliation: Department of Plant and Microbial Biology, University of California Berkeley, Berkeley, CA 94720, USA.
authors.forename: Jonathan K
authors.initials: JK
authors.lastname: Lassila
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Bernstein
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: James N
authors.initials: JN
authors.lastname: Kinney
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Seth D
authors.initials: SD
authors.lastname: Axen
authors.affiliation: Department of Plant and Microbial Biology, University of California Berkeley, Berkeley, CA 94720, USA; Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Berkeley Synthetic Biology Institute, Berkeley, CA 94720, USA; DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA. Electronic address: ckerfeld@lbl.gov.
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Kerfeld
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002451:Cell Compartmentation; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008958:Models, Molecular; D009231:Myxococcales / Q000737:chemistry* / Q000502:physiology* / Q000648:ultrastructure*; D009876:Operon; D015388:Organelles; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary
chemical_list: D001426:Bacterial Proteins
keywords: compartmentalization; metabolic engineering; self-assembly; synthetic biology