Isolated ε subunit of thermophilic F1-ATPase binds ATP

Abstract

F1-ATPase, a soluble part of the F0F1-ATP synthase, has subunit structure α3β3γ δε in which nucleotide-binding sites are located in the α and β subunits and, as believed, in none of the other subunits. However, we report here that the isolated E subunit of F1-ATPase from thermophilic Bacillus strain PS3 can bind ATP. The binding was directly demonstrated by isolating the ε subunit-ATP complex with gel filtration chromatography. The binding was not dependent on Mg2+ but was highly specific for ATP; however, ADP, GTP, UTP, and CTP failed to bind. The ε subunit lacking the C-terminal helical hairpin was unable to bind ATP. Although ATP binding to the isolated ε subunits from other organisms has not been detected under the same conditions, a possibility emerges that the ε subunit acts as a built in cellular ATP level sensor of F0F 1-ATP synthase.