2I4C

Crystal structure of Bicarbonate Transport Protein CmpA from Synechocystis sp. PCC 6803 in complex with bicarbonate and calcium

Summary for 2I4C

• Entry DOI: 10.2210/pdb2i4c/pdb
• Related: 2I48 2I49 2I4B
• Descriptor: Bicarbonate transporter, BICARBONATE ION, CALCIUM ION, ... (4 entities in total)
• Functional Keywords: alpha-beta protein, c-clamp, periplasmic solute-binding protein, abc transporter, bicarbonate, transport protein
• Biological source: Synechocystis sp.
• Cellular location: Cell inner membrane; Peripheral membrane protein (By similarity): Q55460
• Total number of polymer chains: 1
• Total formula weight: 47186.96

Authors

Koropatkin, N.M.,Smith, T.J.,Pakrasi, H.B. (deposition date: 2006-08-21, release date: 2006-12-19, Last modification date: 2023-08-30)

Primary citation

Koropatkin, N.M.,Koppenaal, D.W.,Pakrasi, H.B.,Smith, T.J.
The Structure of a Cyanobacterial Bicarbonate Transport Protein, CmpA.
J.Biol.Chem., 282:2606-2614, 2007

PubMed Abstract: Cyanobacteria, blue-green algae, are the most abundant autotrophs in aquatic environments and form the base of the food chain by fixing carbon and nitrogen into cellular biomass. To compensate for the low selectivity of Rubisco for CO2 over O2, cyanobacteria have developed highly efficient CO2-concentrating machinery of which the ABC transport system CmpABCD from Synechocystis PCC 6803 is one component. Here, we have described the structure of the bicarbonate-binding protein CmpA in the absence and presence of bicarbonate and carbonic acid. CmpA is highly homologous to the nitrate transport protein NrtA. CmpA binds carbonic acid at the entrance to the ligand-binding pocket, whereas bicarbonate binds in nearly an identical location compared with nitrate binding to NrtA. Unexpectedly, bicarbonate binding is accompanied by a metal ion, identified as Ca2+ via inductively coupled plasma optical emission spectrometry. The binding of bicarbonate and metal appears to be highly cooperative and suggests that CmpA may co-transport bicarbonate and calcium or that calcium acts a cofactor in bicarbonate transport.

PubMed: 17121816
DOI: 10.1074/jbc.M610222200

Experimental method

X-RAY DIFFRACTION (1.7 Å)