Chemistry

Amino acid

Receptor

Transmembrane domain

Gene

Biophysics

Transporter

Organic chemistry

Biology

Bicarbonate

Photosynthesis

Transmembrane protein

Biochemistry

Nature Plants

Bicarbonate transporters play essential roles in pH homeostasis in mammals and photosynthesis in aquatic photoautotrophs. A number of bicarbonate transporters have been characterized, among which is BicA—a low-affinity, high-flux SLC26-family bicarbonate transporter involved in cyanobacterial CO2-concentrating mechanisms (CCMs) that accumulate CO2 and improve photosynthetic carbon fixation. Here, we report the three-dimensional structure of BicA from Synechocystis sp. PCC6803. Crystal structures of the transmembrane domain (BicATM) and the cytoplasmic STAS domain (BicASTAS) of BicA were solved. BicATM was captured in an inward-facing HCO3−-bound conformation and adopts a ‘7+7’ fold monomer. HCO3− binds to a cytoplasm-facing hydrophilic pocket within the membrane. BicASTAS is assembled as a compact homodimer structure and is required for the dimerization of BicA. The dimeric structure of BicA was further analysed using cryo-electron microscopy and physiological analysis of the full-length BicA, and may represe...

Structural mechanism of the active bicarbonate transporter from cyanobacteria