Three-dimensional 15N-1H-1H and 15N-13C-1H nuclear-magnetic resonance studies of HPr a central component of the phosphoenolpyruvate-dependent phosphotransferase system from Escherichia coli. Assignment of backbone resonances

We have performed three-dimensional NMR studies on a central component of the phosphoenolpyruvate-dependent phosphotransferase system of Escherichia coli, denoted as HPr. The protein was uniformly enriched with 15N and 13C to overcome spectral overlap. Complete assignments were obtained for the backbone 1H, 15N and 13C resonances, using three-dimensional heteronuclear 1H NOE 1H-15N multiple-quantum coherence spectroscopy (3D-NOESY-HMQC) and three-dimensional heteronuclear total correlation 1H-15N multiple-quantum coherence spectroscopy (3D-TOCSY-HMQC) experiments on 15N-enriched HPr and an additional three-dimensional triple-resonance 1HN-15N-13Cα correlation spectroscopy (HNCA) experiment on 13C,15N-enriched HPr. Many of the sequential backbone 1H assignments, as derived from two-dimensional NMR studies, were corrected. Almost all discrepancies are in the helical regions, leaving the published antiparallel β-sheet topology almost completely intact