The C-terminal two-thirds of the rat liver ATP synthase β subunit has been overexpressed and exported to the Escherichia coli periplasm under the direction of the alkaline phosphatase (phoA) promoter and leader peptide. The processed soluble protein contains the 358 amino acids from glutamate 122 to the rat liver β C-terminal serine 479, including all the regions that have been predicted by chemical and genetic modification studies to be involved in nucleotide, P(i), and Mg2+ binding. Through a simple sequence of Tris/EDTA/lysozyme treatment, osmotic lysis, and alkaline pH washes, the processed β subunit fragment can be prepared in >95% purity and at a yield of >20 mg/liter of culture. It interacts with 2'(3')-O-(2,4,6-trinitrophenyl) adenosine 5'-triphosphate (TNP-ATP) which exhibits a strong enhancement of fluorescence upon binding. A similar enhancement is observed upon interaction with TNP-ADP. Enhancement observed with both TNP-nucleotides is markedly reduced by prior addition of either ATP or ADP and almost completely prevented by the ATP synthase inhibitor 7-chloro-4-nitrobenz-2-oxa-1,3-diazole. Both TNP-ATP and TNP-ADP bind at a stoichiometry of approximately 1 mol of nucleotide/mol of β subunit fragment. Under the same conditions, TNP-AMP does not exhibit a fluorescence enhancement. This work demonstrates that, in the absence of interaction with other ATP synthase subunits, the rat liver β subunit sequence from glutamate 122 to the C terminus exhibits no more than one readily detectable nucleotide binding domain. This success in producing a 'functional' β subunit fragment has significance for the pursuit of genetic and physical studies focused on the structure and function of the rat liver ATP synthase β subunit.
|Original language||English (US)|
|Number of pages||5|
|Journal||Journal of Biological Chemistry|
|State||Published - 1988|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology