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PLoS One. 2013 Sep 4;8(9):e76127. doi: 10.1371/journal.pone.0076127. eCollection 2013.

The bacterial carbon-fixing organelle is formed by shell envelopment of preassembled cargo.

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  • 1Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America ; Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America.

Abstract

BACKGROUND:

Cyanobacteria play a significant role in the global carbon cycle. In Synechococcuselongatus, the carbon-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is concentrated into polyhedral, proteinaceous compartments called carboxysomes.

METHODOLOGY/PRINCIPAL FINDINGS:

Using live cell fluorescence microscopy, we show that carboxysomes are first detected as small seeds of RuBisCO that colocalize with existing carboxysomes. These seeds contain little or no shell protein, but increase in RuBisCO content over several hours, during which time they are exposed to the solvent. The maturing seed is then enclosed by shell proteins, a rapid process that seals RuBisCO from the cytosol to establish a distinct, solvent-protected microenvironment that is oxidizing relative to the cytosol. These closure events can be spatially and temporally coincident with the appearance of a nascent daughter RuBisCO seed.

CONCLUSIONS/SIGNIFICANCE:

Carboxysomes assemble in a stepwise fashion, inside-to-outside, revealing that cargo is the principle organizer of this compartment's biogenesis. Our observations of the spatial relationship of seeds to previously formed carboxysomes lead us to propose a model for carboxysome replication via sequential fission, polymerization, and encapsulation of their internal cargo.

PMID:
24023971
PMCID:
PMC3762834
DOI:
10.1371/journal.pone.0076127
[PubMed - indexed for MEDLINE]
Free PMC Article
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