Secondary structure of the lac repressor DNA-binding domain by two-dimensional 1H nuclear magnetic resonance in solution.

A recently proposed approach for spatial structure determination in noncrystalline proteins by nuclear magnetic resonance was applied to the lac repressor DNA-binding domain. On the basis of sequence-specific 1H NMR assignments, the location of alpha-helices in the amino acid sequence was determined from nuclear Overhauser enhancement data and from amide proton exchange studies. These investigations provide detailed experimental data on the structure of a noncrystalline DNA-binding protein. The results support the hypothesis advanced by others that sequence-specific interactions between lac repressor and DNA are mediated by a particular spatial arrangement of two alpha-helices common to various different DNA-binding proteins.