Proton nuclear magnetic resonance assignments and secondary structure determination of the ColE1 rop (rom) protein

The complete resonance assignment of the ColE1 rop (rom) protein at pH 2.3 was obtained by two-dimensional (2D) proton nuclear magnetic resonance spectroscopy (1H NMR) at 500 and 600 MHz using through-bond and through-space connectivities. Sequential assignments and elements of regular secondary structure were deduced by analysis of nuclear Overhauser enhancement spectroscopy (NOESY) experiments and 3JHN alpha coupling constants. One 7.2-kDa monomer of the homodimer consists of two antiparallel helices connected by a hairpin loop at residue 31. The C-terminal peptide consisting of amino acids 59-63 shows no stable conformation. The dimer forms a four-helix bundle with opposite polarization of neighboring elements in agreement with the X-ray structure.