Study of the interactions of atypical subunit ASA1 in the ATP synthase of Polytomella sp.

The mitochondrial ATP synthase of chlorophycean algae has a structure different from that of other organisms. All the subunits that typically make up the the peripheral arm and those that are involved in the dimerization of the enzyme are missing. In compensation, it has acquired nine subunits of unknown evolutionary origin that have been named ASA1 to ASA9. These ASA subunits are only present in chlorophycean algae and are not found in others closely related algal lineages, such as ulvophycean, prasynophycean and trebuxophycean green algae. Heat dissociation experiments, cross linking studies and electronic microscopy studies have allowed the proposal of a structural model of the ATP synthase of chlorophycean algae in which ASA subunits make up the peripheral arm and participate in the dimerization of the enzyme; however, the localization of ASA1 subunit remains unclear. The objective of this work is to clone and purify the ASA1 subunit to perform interaction studies in order to know which are its neighboring subunits and to propose its topological disposition in the peripheral arm of the ATP synthase of Polytomella sp. The experimental strategy is based on the cloning of the corresponding gene, the overexpression of the protein in Escherichia coli and the purification of the recombinant protein in order to perform interaction assays. In this work, we report an ASA1-OSCP interaction, which could link a classical protein of the enzyme, such as OSCP, with an atypical subunit unique to the chlorophycean algal lineage.