Part:BBa_K2078000
cmpA
The CmpA gene forms the first part of the CmpABCD operon, which codes for a bicarbonate transporter. It encodes the substrate-binding protein of the transporter and plays a crucial role in the carbon-concentrating machinery of synechocystis.
Function
The CmpA protein is used to transport bicarbonate ions (HCO3-) into the carboxysome, an organelle that contains Rubisco. The HCO3- is then converted into CO2. This mechanism allows synechocystis to concentrate CO2 in the carboxysome around Rubisco and exclude O2, for which Rubisco also has a high affinity. The concentration of CO2 inside the carboxysome can be up to 1000 times higher than in the cytoplasm, resulting in a significant increase in photosynthetic efficiency.
Structure
CmpA is an α-ß protein similar in structure to the nitrate transporter NrtA. It consists of two domains arranged in a C-clamp shape around the ligand-binding site. Both of these domains contain a central complex of five-stranded ß-pleated sheets surrounded by α-helices. They are joined to each other by a sheaf of irregularly coiled elements. The entire protein is anchored to the plasma membrane by a lipid; CmpA is a member of the periplasmic-binding protein superfamily.
Mechanism
Bicarbonate ions bind to the ligand-binding site contained within the cleft formed by the two α-ß domains. These two domains then wrap around the ligand. This involves only minor conformational changes; the ligand-binding site is fairly inflexible. It should be noted that the binding of bicarbonate is coupled to the binding of Ca2+. The two ions bind co-operatively with high affinity. It is thought that Ca2+ may act as a cofactor.
Usage and Biology
CLSB_UK_2016
The part was tested in Synechocystis (using pDF-lac plasmid and it's own constitutive, strong promoter) by measuring the growth rate. It showed a doubling of the growth rate during the exponential stage as illustrated by the graph below. The initial delay could be either due to different starting concentrations of the cyanobacteria in the culture or due to the effect of the low-copy number of the pDF-lac plasmid. Growth curve was measured using a colorimeter at 680nm and confirmed by measuring the OD.
References
Koropatkin NM, Koppenaal DW, Pakrasi HB, Smith TJ. 2007. The structure of a cyanobacterial bicarbonate transport protein, CmpA. J. Biol. Chem. 282:2606–2614
Raven, J.A., Cockell, C.S., De La Rocha, C.L., 2008. The evolution of inorganic carbon 69 concentrating mechanisms in photosynthesis. Philos. Trans. R. Soc. B: Biol. Sci. 363, 2641-2650
Maeda S, Price GD, Badger MR, Enomoto C, Omata T. 2000. Bicarbonate binding activity of the CmpA protein of the cyanobacterium Synechococcus sp. strain PCC 7942 involved in active transport of bicarbonate. J. Biol. Chem. 275:20551–20555
Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12COMPATIBLE WITH RFC[12]
- 21COMPATIBLE WITH RFC[21]
- 23COMPATIBLE WITH RFC[23]
- 25INCOMPATIBLE WITH RFC[25]Illegal NgoMIV site found at 95
Illegal AgeI site found at 128
Illegal AgeI site found at 281 - 1000COMPATIBLE WITH RFC[1000]
//chassis/prokaryote/cyanobacterium
chassis | Synechocystis sp. PCC6803 |