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A Guide to Production, Crystallization, and Structure Determination of Human IKK1/α
Published on: November 2, 2018
A dodecameric CcmK2 structure suggests β-carboxysomal shell facets have a double-layered organization
Bożena Samborska1, Matthew S Kimber
1Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
Structure (London, England : 1993)
|July 4, 2012
Summary
Cyanobacteria use carboxysomes for carbon fixation. The beta-carboxysome shell, built from CcmK proteins, is likely a double layer, based on CcmK2
Area of Science:
- Biochemistry
- Structural Biology
- Microbiology
Background:
- Cyanobacteria perform carbon fixation within specialized organelles called carboxysomes.
- Carboxysomes are enclosed by a protein shell composed of CcmK proteins, which encapsulates key enzymes like RubisCO and carbonic anhydrase.
- Previous models suggested carboxysome shells might be single-layered.
Purpose of the Study:
- To investigate the structural organization of the beta-carboxysome shell in Thermosynechococcus elongatus.
- To determine the interaction mechanisms of CcmK paralogs, particularly CcmK2, in shell formation.
- To elucidate whether the carboxysome shell is a single or double layer.
Main Methods:
- Fluorescence Resonance Energy Transfer (FRET) was employed to quantify interactions between CcmK paralogs.
- Structural analysis of CcmK2 was performed.
- Computational modeling was used to predict shell assembly based on observed CcmK2 interactions.
Main Results:
- CcmK2, a highly abundant CcmK paralog, exhibits strong self-interactions mediated by a specific helical region (residues 95-101).
- The crystal structure of CcmK2 revealed a back-to-back dodecameric arrangement.
- Modeling based on CcmK2 dodecamers predicted seamless fusion of two sheets into a double-layered shell, consistent with experimental FRET data and observed shell thickness.
Conclusions:
- The beta-carboxysome shell is most likely organized as a double layer of CcmK proteins.
- CcmK2 dodecamers play a crucial role in forming the double-layered structure.
- This finding refines our understanding of carboxysome biogenesis and structure.
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