Engineering the membrane rotor ring of ATP synthases involved in photosynthesis

In the light dependent reactions of photosynthesis, ATP synthase couples the translocation of protons across the thylakoid membrane with the synthesis of ATP molecules. The structure and mechanism of several ATP synthases is understood and it is now possible to attempt to engineer this enzyme to improve its efficiency.

Bacterial and chloroplastic ATP synthases consist of eight or nine different subunits and can be subdivided into two subcomplexes: the F1water-soluble, catalytic head and the Fo membrane-embedded rotor. A key component of Fo is the membrane rotor ring, also known as the c-ring, composed of several copies of the c-subunit. A single c-subunit monomer is a hairpin of two transmembrane a-helices. The number of c-subunits that form the c-ring is known as the c-ring stoichiometry and is equal to the number of ions translocated per full rotation of the rotor; with three molecules of ATP synthesised per 360 rotation. The stoichiometry is constant within a given species but variable across different species, reflecting the different bioenergetic demands placed on each species. Furthermore, it has been demonstrated that the c-ring stoichiometry is determined by the primary structure of the c-subunit and certain mutations introduced can alter the stoichiometries in bacterial ATP synthases.

In this project, the aim is to engineer the stoichiometry of the c-rings of ATP synthases involved in the light-dependent reactions of photosynthesis. Mutant ATP synthases will be compared to the wild-type at the molecular and cellular level. The ATP molecules synthesised in the light dependent reactions are required for the subsequent carbon fixation reactions of photosynthesis and mutant ATP synthases capable of more efficient ATP production under certain cell physiological conditions may have biotechnological applications in agriculture.