HETERONUCLEAR H-1-N-15 NUCLEAR-MAGNETIC-RESONANCE STUDIES OF THE C-SUBUNIT OF THE ESCHERICHIA-COLI F1F0 ATP SYNTHASE - ASSIGNMENT AND SECONDARY STRUCTURE

Nuclear magnetic resonance (NMR) studies of the c subunit of F1F(o) ATP synthase from Escherichia coli are presented. A combination of homonuclear (H-1-H-1) and heteronuclear (H-1-N-15) 2D and 3D methods was applied to the 79-residue protein, dissolved in trifluoroethanol. Resonance assignment for all the backbone amide groups and many C(alpha)H side-chain protons was achieved. Analysis of inter- and intraresidue H-1-H-1 nuclear Overhauser effect (NOE) data and scalar coupling constant information indicates that this protein contains two extended regions of predominant alpha-helical character (residues 10-40 and 48-77) separated by an eight-residue segment which displays little evidence of ordered secondary structure. This model is consistent with information about the molecular motion of the protein deduced from N-15-H-1 heteronuclear NOE data and observed pK(a) values of carboxylic acid groups.