Structure and function of cyanobacterial bicarbonate transporters

Dr Dean Price (RSBS)
in association with
Dr Susan Howitt (BaMBi)

The Price lab (RSBS) is studying photosynthetic acquisition of inorganic carbon (CO2 and HCO3-) in several cyanobacterial species. This efficient adaptation is known as a CO2 concentrating mechanism (CCM) since it results in elevation of CO2 around the primary carboxylase, Rubisco. This allows photosynthetic CO2 fixation to occur even when the external concentration of inorganic carbon would normally limit growth. The cyanobacterial CCM features active transporters for CO2 and HCO3-, and many of these systems have been genetically and physiologically identified in the Price lab. The study of CO2 acquisition by cyanobacteria is a fundamentally important process. It is estimated that around 45% of global primary productivity occurs in the world’s oceans, with cyanobacterial species responsible for more than half of this oceanic productivity.

Structure and function of bicarbonate transporters from marine cyanobacteria

The Price lab has recently discovered a new class of HCO3- transporter that belongs to the SulP family (see Susan Howitt’s entry). The new transporter is termed BicA and has been shown to be Na+-dependent. Part of the characterisation process involves expressing genes from a shuttle vector that replicates in the well characterised freshwater strain, Synechococcus PCC7942. We have so far characterised two BicA transporters from marine cyanobacteria and find that their flux rates and affinity for HCO3- vary considerably. An objective of the project is clone and characterise BicA homologs from other marine cyanobacteria (there are currently 8 sequenced marine species). These will also be compared to some interesting BicA homologs from soil bacteria. Another objective is to employ bioinformatics to identify specific residues that may be involved in directing substrate affinity and flux rate.

This project would involve the construction of plasmid expression vectors. Functional analysis of mutants will include measurement of HCO3- uptake using membrane inlet mass spectrometry and analysis of transporter expression using specific tag antibodies. The project will utilise both molecular biology (mutagenesis, DNA sequencing, PCR) and biochemistry (transport assays, membrane isolation and Western blotting).

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