Pressure-induced changes in the folded structure of lysozyme.

We demonstrate, for the first time in solution, that pressure induces changes in the overall folded structure of a protein (lysozyme). This was made possible by using a home-developed, on-line continuously variable pressure cell on a high resolution NMR spectrometer operating at 750 MHz. We could follow pressure-induced diamagnetic chemical shifts of more than 26 protons of lysozyme at variable pressure in the range of 1 to 2000 bar. The results indicate that the main effect of the pressure is a compaction of the hydrophobic core part of the protein consisting of bulky side-chains. The technique introduced here provides a general method with which one can probe microscopic internal flexibility of a protein in solution.