Over-expression of the β-carboxysomal CcmM protein in Synechococcus PCC7942 reveals a tight co-regulation of carboxysomal carbonic anhydrase (CcaA) and M58 content

Photosynth Res. 2011 Sep;109(1-3):33-45. doi: 10.1007/s11120-011-9659-8. Epub 2011 May 20.

Abstract

Carboxysomes, containing the cell's complement of RuBisCO surrounded by a specialized protein shell, are a central component of the cyanobacterial CO(2)-concentrating mechanism. The ratio of two forms of the β-carboxysomal protein CcmM (M58 and M35) may affect the carboxysomal carbonic anhydrase (CcaA) content. We have over-expressed both M35 and M58 in the β-cyanobacterium Synechococcus PCC7942. Over-expression of M58 resulted in a marked increase in the amount of this protein in carboxysomes at the expense of M35, with a concomitant increase in the observed CcaA content of carboxysomes. Conversely, M35 over-expression diminished M58 content of carboxysomes and led to a decrease in CcaA content. Carboxysomes of air-grown wild-type cells contained slightly elevated CcaA and M58 content and slightly lower M35 content compared to their 2% CO(2)-grown counterparts. Over a range of CcmM expression levels, there was a strong correlation between M58 and CcaA content, indicating a constant carboxysomal M58:CcaA stoichiometry. These results also confirm a role for M58 in the recruitment of CcaA into the carboxysome and suggest a tight regulation of M35 and M58 translation is required to produce carboxysomes with an appropriate CA content. Analysis of carboxysomal protein ratios, resulting from the afore-mentioned over-expression studies, revealed that β-carboxysomal protein stoichiometries are relatively flexible. Determination of absolute protein quantities supports the hypothesis that M35 is distributed throughout the β-carboxysome. A modified β-carboxysome packing model is presented.

MeSH terms

  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Carbon Dioxide / metabolism
  • Carbonic Anhydrases / genetics
  • Carbonic Anhydrases / metabolism*
  • Gene Expression Regulation, Bacterial
  • Gene Expression Regulation, Enzymologic
  • Models, Molecular
  • Organelles / enzymology
  • Organelles / genetics
  • Organelles / metabolism*
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Ribulose-Bisphosphate Carboxylase / genetics
  • Ribulose-Bisphosphate Carboxylase / metabolism
  • Sequence Deletion
  • Synechococcus / enzymology
  • Synechococcus / genetics
  • Synechococcus / metabolism*

Substances

  • Bacterial Proteins
  • Recombinant Fusion Proteins
  • Carbon Dioxide
  • Ribulose-Bisphosphate Carboxylase
  • Carbonic Anhydrases