High Pressure Effects on Protein Flexibility as Monitored by Tryptophan Phosphorescence

Hydrostatic pressure is a modulator of biochemical processes: it inhibits bacterial growth, activates/inactivates enzymatic reactions. The application of high pressure above 3–4 kbar induces protein denaturation, whereas in the range between 1–2 kbar compression induces dissociation of oligomers[1]. It is commonly accepted that protein conformation is invariant to pressure and that inhibition of biological activity in the pre-denaturant range is due to the dissociation of oligomeric enzymes. But in recent years it has been proposed that inhibition of biological activity at moderate non-denaturating pressures might be due to the reduced flexibility of proteins rather than to the dissociation [2]. Up to date little is known about pressure effects on protein flexibility. In this paper we describe the use of the exquisite sensitivity of the phosphorescence lifetime of tryptophan to the fluidity of the environment to monitor changes in flexibility of several proteins under pressure. The results point out also important pressure-induced predissociational and post dissociational changes of protein structure