Rapid changes in hydrostatic pressure as a probe for correlating function of purified proteins with their measured activity in living cells.

Hydrostatic pressure (HP) has long been used to perturb protein and membrane structures and to alter their interactions with binding partners in a fully reversible manner. HP has also long been used to perturb molecular structures in living cells, where it can alter cytoskeleton dynamics and cellular signalling pathways and to stall cell division in a wide variety of cell types. HP can be applied and removed in a fraction of a second and is transmitted through tissue at the speed of sound; thus, rapid changes in HP can be very useful to correlate the behaviour of isolated macromolecules with the same molecules within living cells. Despite its usefulness, HP has not found wide use among researchers, mainly because of the need for specialist equipment. This largely reflects the use of high HP (≥ 1000 atmospheres) by the majority of practitioners. While these high pressures have provided insights into protein denaturation, membrane reorganisation, and sterilisation of bacteria and viruses in medicine and food, here we will focus on the uses of moderate HP (< 200 atmospheres) where the engineering and safety issues are less significant. At these lower pressures, HP alters the water shells at molecular interfaces. We outline here the background of the methods used and some of the simple adaptations required to laboratory equipment to allow HP studies and give some examples of its use for studying isolated proteins and the same proteins in living cells.