Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 396, Issue 1, Pages 105-117Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2009.11.019
Keywords
H. neapolitanus; bacterial microcompartment; carboxysome; cryo-EM; electron tomography
Categories
Funding
- National Institutes of Health [R01 AI067548, P50 GM082545]
- Department of Energy [DE-FG02-04ER63785]
- National Science Foundation [MCB-0818680]
- Beckman Institute at Caltech
- Div Of Molecular and Cellular Bioscience
- Direct For Biological Sciences [0818680] Funding Source: National Science Foundation
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Carboxysomes are polyhedral inclusion bodies that play a key role in autotrophic metabolism in many bacteria. Using electron cryotomography, we examined carboxysomes in their native states within intact cells of three chemolithoautotrophic bacteria. We found that carboxysomes generally cluster into distinct groups within the cytoplasm, often in the immediate vicinity of polyphosphate granules, and a regular lattice of density frequently connects granules to nearby carboxysomes. Small granular bodies were also seen within carboxysomes. These observations suggest a functional relationship between carboxysomes and polyphosphate granules. Carboxysomes exhibited greater size, shape, and compositional variability in cells than in purified preparations. Finally, we observed carboxysomes in various stages of assembly, as well as filamentous structures that we attribute to misassembled. shell protein. Surprisingly, no more than one partial carboxysome was ever observed per cell. Based on these observations, we propose a model for carboxysome assembly in which the shell and the internal RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) lattice form simultaneously, likely guided by specific interactions between shell proteins and RuBisCOs. (C) 2009 Elsevier Ltd. All rights reserved.
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