Solution Structure of Subunit F6 from the Peripheral Stalk Region of ATP Synthase from Bovine Heart Mitochondria

The ATP synthase enzyme structure includes two stalk assemblies, the central stalk and the peripheral stalk. Catalysis involves rotation of the central stalk assembly together with the membrane-embedded ring of c-subunits driven by the trans-membrane proton-motive force, while the α and β-subunits of F1 are prevented from co-rotating by their attachment to the peripheral stalk. In the absence of structures of either the intact peripheral stalk or larger complexes containing it, we are studying its individual components and their interactions to build up an overall picture of its structure. Here, we describe an NMR structural characterisation of F6, which is a 76-residue protein located in the peripheral stalk of the bovine ATP synthase and is essential for coupling between the proton-motive force and catalysis. Isolated F6 has a highly flexible structure comprising two helices packed together through a loose hydrophobic core and connected by an unstructured linker. Analysis of chemical shifts, 15N relaxation and RDC measurements confirm that the F6 structure is flexible on a wide range of timescales ranging from nanoseconds to seconds. The relationship between this structure for isolated F6 and its role in the intact peripheral stalk is discussed.