This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Supplemental material
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowReprints and Permissions
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Cot, S. S.-W.
Right arrow Articles by Espie, G. S.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Cot, S. S.-W.
Right arrow Articles by Espie, G. S.

 Previous Article  |  Next Article 

Journal of Bacteriology, February 2008, p. 936-945, Vol. 190, No. 3
0021-9193/08/$08.00+0     doi:10.1128/JB.01283-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

A Multiprotein Bicarbonate Dehydration Complex Essential to Carboxysome Function in Cyanobacteria{triangledown} ,{dagger}

Swan S.-W. Cot, Anthony K.-C. So, and George S. Espie*

Department of Biology, University of Toronto, Mississauga, Mississauga, Ontario L5L 1C6, Canada

Received 8 August 2007/ Accepted 5 November 2007

Carboxysomes are proteinaceous biochemical compartments that constitute the enzymatic "back end" of the cyanobacterial CO2-concentrating mechanism. These protein-bound organelles catalyze HCO3– dehydration and photosynthetic CO2 fixation. In Synechocystis sp. strain PCC6803 these reactions involve the β-class carbonic anhydrase (CA), CcaA, and Form 1B ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The surrounding shell is thought to be composed of proteins encoded by the ccmKLMN operon, although little is known about how structural and catalytic proteins integrate to form a functional carboxysome. Using biochemical activity assays and molecular approaches we have identified a catalytic, multiprotein HCO3– dehydration complex (BDC) associated with the protein shell of Synechocystis carboxysomes. The complex was minimally composed of a CcmM73 trimer, CcaA dimer, and CcmN. Larger native complexes also contained RbcL, RbcS, and two or three immunologically identified smaller forms of CcmM (62, 52, and 36 kDa). Yeast two-hybrid analyses indicated that the BDC was associated with the carboxysome shell through CcmM73-specific protein interactions with CcmK and CcmL. Protein interactions between CcmM73 and CcaA, CcmM73 and CcmN, or CcmM73 and itself required the N-terminal {gamma}-CA-like domain of CcmM73. The specificity of the CcmM73-CcaA interaction provided both a mechanism to integrate CcaA into the fabric of the carboxysome shell and a means to recruit this enzyme to the BDC during carboxysome biogenesis. Functionally, CcaA was the catalytic core of the BDC. CcmM73 bound H14CO3– but was unable to catalyze HCO3– dehydration, suggesting that it may potentially regulate BDC activity.

* Corresponding author. Mailing address: Department of Biology, University of Toronto, Mississauga, 3359 Mississauga Rd, Mississauga, Ontario L5L 1C6, Canada. Phone: (905) 828-5380. Fax: (905) 828-3792. E-mail: george.espie{at}utoronto.ca

{triangledown} Published ahead of print on 9 November 2007.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, February 2008, p. 936-945, Vol. 190, No. 3
0021-9193/08/$08.00+0     doi:10.1128/JB.01283-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





Copyright © 2009 by the American Society for Microbiology.   For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»