High-resolution proton nuclear magnetic resonance studies of the exchangeable resonances of the lac repressor headpiece.

Abstract

The exchangeable hydrogens of the N-terminal 51 amino acid headpiece (HP) of the lac repressor have been examined with high-resolution 1H NMR. Resonances from 35 +/- 3 protons are observable in 2H2O solutions at p2H 4.2. The exchange rates for some of these have been measured over the p2H range 1.5-5. In H2O, resonances from 70 +/- 6 protons are observable at pH 3.2 and 35 +/- 5 protons at pH 7.1. The temperature dependence of the spectrum at neat neutral pH shows the existence of a group of approximately 22 protons particularly slow to exchange. The pH dependence of the spectrum in H2O solution over the range 1-11 is discussed. Results are compared with NMR studies of the nonexchanging protons and CD and IR results.