Protein-Lipid Interactions of the Proteolipid c Subunit of the Escherichia coli Proton-Translocating Adenosinetriphosphatase

Interactions between Escherichia coli membrane phospholipids and the hydrophobic c subunit of the F1F0 proton-translocating ATPase were characterized. Extraction of E. coli membranes with a neutral mixture of chloroform and methanol and subsequent separation steps produced several protein-containing fractions. The protein-containing fraction most soluble in organic solvents contained subunit c and a lipid fraction enriched in phosphatidylglycerol compared to total E. coli membrane phospholipids. Other ATPase subunits and some additional proteins extracted from the membranes by this procedure could be separated from the c subunit by subsequent extraction. The purified and delipidated c subunit contained fatty acids which were released upon treatment with boron trifluoride methanol. Furthermore, deleting and restoring the genes for the F0 subunits changed the composition of extractable membrane phospholipid and fatty acids, indicating that the F0 plays a significant structural role in the membrane.