1H Nuclear Magnetic Resonance Studies of an Integral Membrane Protein: Subunit C of the F1F0 ATP Synthase

The membrane-traversing subunit c parallel from the F0 part of the ATP synthase molecule has been studied in chloroform/methanol by high-resolution 1H n.m.r. Various one-dimensional and two-dimensional techniques have been used for assignment purposes, some NOE connectivities were established and some 3JHN alpha coupling constants were measured from spin--echo experiments. The effects of varying pH, solvent composition, lanthanide concentration and temperature have been investigated. Evidence is presented that the molecule has extensive alpha-helical segments, and the hairpin structure suggested by other groups is supported by our n.m.r. data. Only one ionizable group, assigned to the C-terminal carboxyl, is observed to titrate in the pH range 2 to 10; so the conserved residue, Asp61, which binds dicyclohexylcarbodiimide, presumably has (at least in this solvent system) an abnormally high pK value.