The deep-sea in our planet is characterized as the extreme world placed under high-hydrostatic pressure. We have identified many of living creatures in the deep-sea environment, and several high-pressure loving organisms, called “piezophiles”, have been found and isolated using the manned and unmanned deep-sea submersible systems. Then, this extreme world is being more and more elucidated. In this article, the fascination to investigate the mysterious world, deep-sea, is introduced, then, the strategies for adaptation to the high-pressure condition in microorganisms are illustrated at the molecular levels. Finally, the next stage to study the pressure life science would be discussed.
Pressure and temperature are fundamental physical parameters to control molecular properties and equilibria of systems. However, pressure approaches to life science are still very limited compared with temperature, due probably to their technical difficulties. Here, nuclear magnetic resonance (NMR) approaches combined with hydrostatic pressure and gas pressure are reviewed. Using NMR spectroscopy with variable pressure is a useful method for characterizing conformational fluctuation of proteins. Gas-pressure NMR spectroscopy using molecular oxygen provides a general and highly sensitive method for detecting internal hydrophobic cavities, which might be sources of protein's conformational fluctuation.
High-pressure protein X-ray crystallography (HPPX) is a unique method that provides high-resolution structural information under various pressure conditions including hydration waters at a molecular surface and internal cavities. Two important applications of HPPX are (1) studying the mechanism of pressure tolerance of proteins from several organisms living in deep seas and (2) observation of functional sub-states of biological macromolecules. After brief introduction, two examples of the recent advances are described in this article. The first one is the study on the mechanism of pressure tolerance of 3-isopropylmalate dehydrogenase from high-pressure adapted deep-sea organisms. The second example is the observation of pressure-induced conformational substate of hen egg white lysozyme, which reveals a part of the reaction mechanism of the enzyme.
High-pressure electrophoresis was designed to investigate the association system of proteins quantitatively. In this methodology, pressure and temperature precisely perturbs the association equilibrium of supermolecular protein assembly, whose decomposed fractions can be in-situ analyzed by native polyacrylamide gel electrophoresis (PAGE). The bands of these fractions allow us not only to unravel the elementary process of assembly formation but also to quantify various volumetric properties including thermal expansion change of each process. In this article, we report its application to the problem of amyloid protofibril formation.
We applied a cubic anvil press which was originally developed for physical and geophysical research to a biological study of search for lives under very high pressure of several GPa order or more. All the animals and plants which have been tested, tardigrades at cryptobiotic state, eggs of plankton, spores of mosses and seeds of same plants, were found alive after exposure to the hydrostatic pressure of 7.5 GPa for at least 1 h. It is un-understandable that actually living creatures can withstand such a very high pressure.
If high hydrostatic pressure (HP) processing is applied for fermented-foods manufacturing to prevent the over-fermentation, the resulting fermented foods could retain more of fresh flavor and nutrient contents. For this pressure-regulated fermentation (PReF) technique, HP-sensitive (piezosensitive) strains, which show remarkable loss of viability during lower pressure levels, would be desirable for the fermentation process. We have generated piezosensitive mutants, as well as a piezotolerant mutant, from a budding yeast Saccharomyces cerevisiae (S. cerevisiae) by ultra-violet mutagenesis. Analyses on the piezosensitivity using the mutants indicated that the piezotolerance of S. cerevisiae was closely related to mitochondrial functions in anaerobic energy metabolism. Deficient in COX1 gene, which is located in mitochondrial DNA encoding a protein in electron transport chain, was demonstrated to achieve a remarkable piezosensitivity. The results would be important for further generation of piezosensitive mutants and their application for fermentation-food manufacturing toward development of PReF technique.
High pressure can accelerate post-mortem aging of meat, which results in improving meat tenderness. High hydrostatic pressure modifies conformation of intramuscular protein molecules, disorganizes the supermolecular structure, and then induces the structural weakening of myofibrils and intramuscular connective tissue. Although the effect of high-pressure processing on meat tenderizations is limited after cooking of meat, combining high pressure with sodium hydrogen carbonate treatments can improve texture and palatability of cooked meat and meat products. Science and technology of the high pressure processing for meat texture will be reviewed.