Multinuclear NMR studies of the trp-repressor.

The binding of the corepressor, L-tryptophan, to the Escherichia coli trp-aporepressor in solution has been examined by 13C- and 19F-NMR spectroscopy. The binding of a number of tryptophan analogues have been studied by equilibrium dialysis. Evidence is presented that support the crystallographic studies (Schevitz, R. W., Otwinowski, Z., Joachimiak, A., Lawson, C. L. and Sigler, P. B. (1985) Nature 317, 782-786) that Val-58 is within the ring currents of the bound tryptophan and also close in space to the indole 5'-position, on the basis of heteronuclear 19F(1H)-NOE experiments. The tryptophan carboxylate is in hydrogen-bonding distance to a highly positively charged residue, probably Arg-54 and this bond strengthens on formation of the trp-repressor-DNA complex.