Pressure effect on the structure of the Tet repressor protein TetR(B)

The fluorescence of two single tryptophan (trp) mutants of the TetR(B)dimer protein was monitored for hydrostatic pressures 0.1 MPa < p < 300 MPa. In mutant W170, in which trp interacts with segments of both subunits, the fitted fluorescence lifetimes vary both with pressure and observation wavelength. In contrast, the lifetimes are fairly independent of both parameters in the case of W171, in which trp is completely solvent exposed. This difference in fluorescence behaviour is in agreement with the fact that only trp 170 experiences a strong alteration of its direct environment upon a movement of alpha-helix 9 induced by increasing static pressure. The conformational changes induced by pressure in this protein region are only partly reversible. After pressure release, the originally more solvent exposed trp 171 ends up, at least in part, in a more solvent shielded environment and the originally protein embedded trp 170 ends up in a more solvent exposed conformation. These observations provide evidence for heterogeneity in chromophore-protein arrangement under normal, biologically relevant conditions. Furthermore, they indicate that no complete dissociation into monomers occurs at pressures below 300 MPa.