title: Characterisation of cyanobacterial bicarbonate transporters in E. coli shows that SbtA homologs are functional in this heterologous expression system.
abstract: Cyanobacterial HCO3(-) transporters BCT1, SbtA and BicA are important components of cyanobacterial CO2-concentration mechanisms. They also show potential in applications aimed at improving photosynthetic rates and yield when expressed in the chloroplasts of C3 crop species. The present study investigated the feasibility of using Escherichia coli to assess function of a range of SbtA and BicA transporters in a heterologous expression system, ultimately for selection of transporters suitable for chloroplast expression. Here, we demonstrate that six β-forms of SbtA are active in E. coli, although other tested bicarbonate transporters were inactive. The sbtA clones were derived from Synechococcus sp. WH5701, Cyanobium sp. PCC7001, Cyanobium sp. PCC6307, Synechococcus elongatus PCC7942, Synechocystis sp. PCC6803, and Synechococcus sp. PCC7002. The six SbtA homologs varied in bicarbonate uptake kinetics and sodium requirements in E. coli. In particular, SbtA from PCC7001 showed the lowest uptake affinity and highest flux rate and was capable of increasing the internal inorganic carbon pool by more than 8 mM relative to controls lacking transporters. Importantly, we were able to show that the SbtB protein (encoded by a companion gene near sbtA) binds to SbtA and suppresses bicarbonate uptake function of SbtA in E. coli, suggesting a role in post-translational regulation of SbtA, possibly as an inhibitor in the dark. This study established E. coli as a heterologous expression and analysis system for HCO3(-) transporters from cyanobacteria, and identified several SbtA transporters as useful for expression in the chloroplast inner envelope membranes of higher plants.
authors.affiliation: Plant Science Division, Realizing Increased Photosynthetic Efficiency (RIPE) Network, Research School of Biology, Linnaeus Building #134, Australian National University, Canberra, ACT 2601, Australia.
authors.forename: Jiahui
authors.initials: J
authors.lastname: Du
authors.affiliation: Plant Science Division, Realizing Increased Photosynthetic Efficiency (RIPE) Network, Research School of Biology, Linnaeus Building #134, Australian National University, Canberra, ACT 2601, Australia.
authors.forename: Britta
authors.initials: B
authors.lastname: Förster
authors.affiliation: Plant Science Division, Realizing Increased Photosynthetic Efficiency (RIPE) Network, Research School of Biology, Linnaeus Building #134, Australian National University, Canberra, ACT 2601, Australia.
authors.forename: Loraine
authors.initials: L
authors.lastname: Rourke
authors.affiliation: Plant Science Division, Realizing Increased Photosynthetic Efficiency (RIPE) Network, Research School of Biology, Linnaeus Building #134, Australian National University, Canberra, ACT 2601, Australia.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Howitt
authors.affiliation: Plant Science Division, Realizing Increased Photosynthetic Efficiency (RIPE) Network, Research School of Biology, Linnaeus Building #134, Australian National University, Canberra, ACT 2601, Australia.
authors.forename: G Dean
authors.initials: GD
authors.lastname: Price
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D046940:Synechococcus / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D001639:Bicarbonates; D002352:Carrier Proteins