NMR studies of the Escherichia coli trp aporepressor. Sequence-specific assignment of the aromatic proton resonances

The resonances in the aromatic region of the 1H-NMR spectrum of the Escherichia coli trp aporepressor have been assigned to amino acid type by two-dimensional correlated spectroscopy (COSY), homonuclear Hartmann-Hahn (HOHAHA) spectroscopy and nuclear Overhauser enhancement spectroscopy (NOESY) techniques and studies of the pH dependence of the chemical shifts, in combination with selective deuteration of the protein. Complete sequence-specific assignments of the aromatic resonances have been made by comparing the observed inter-residue NOEs with those expected on the basis of the crystal structure of the protein [Zhang, R.-G., Joachimiak, A., Lawson, C. L., Shevitz, R. W., Otwinowski, Z. & Sigler, P. B. (1987) Nature 327, 591–597]. The latter experiments have also permitted the sequence-specific assignment of some of the high-field methyl resonances. The complete assignment of the aromatic region of the spectrum, in particular of resonances from residues at the dimer interface, opens the way to detailed studies of the conformational effects of corepressor and operator binding.