Research performed 1989--1993 with Prof. Rainer Jaenicke at the
Institute for Biophysics and Physical Biochemistry,
For a review see ref. .
For a more general account of research into life under extreme conditions see Life on the Edge.
The pressure induced dissociation of ribosomes has hitherto been considered a major cause for the pressure-sensitivity of non-adapted micro-organisms. This assumption relies on data from the 1970s, when the knowledge about ribosomes had not yet reached the molecular level. When reinvestigating the issue with the help of current knowledge about ribosomes and protein biosynthesis I found that the pronounced pressure-sensitivity of highly purified ribosomes can be decreased by choosing an appropriate buffer system, which has been derived from a hepes/polyamine buffer optimized for in vivo- like performance in in vitro protein biosynthesis. Furthermore, functional ribosomal complexes representing elongation cycle intermediates are stable over the whole range of pressures occuring in the biosphere (1 - 1000 bar). Thus, the sensitivity of bacterial protein biosynthesis and other vital functions must be attributed to a cause different from the dissociation of ribosomes. I put forward the "compression hypothesis", which states that flexible, loosely packed regions of the ribosomal particles become more densely packed and more rigid by the effect of hydrostatic pressure. This effect would slow down and eventually inhibit the functionally important motions inside the molecular machinery. In order to verify this hypothesis with smaller model systems, I studied the effects of pressure on the activity of monomeric enzymes (lysozyme, trypsin, thermolysin, octopin dehydrogenase). The latter shows a complex behaviour, which may well be interpreted in terms of an inhibition by compression.
A similar problem is found in the field of pressure effects on crystallization, which has not been studied systematically before the beginning of this work. The inhibitory effect may be explained either by an equilibrium shift in the nucleation reaction, or by a conformational alteration induced by hydrostatic pressure. I have been able to show that all of the apparently contradicting results concerning the effects of pressure on lysozyme crystallization may be explained by the Oosawa theory of protein self-assembly, if a rapid pre-equilibrium between two species is introduced, of which only one can be incorporated into crystallization nuclei or growing crystals.
Concerning the in vivo side of the adaptation problem, I investigated the effect of pres- sure on the protein expression of marine fungi by two-dimensional electrophoresis. Apparently, one has to approach the limit of lethal pressures (500 bar) in order to induce the expression of "pressure adaptation proteins", which seems to be correlated to the occurence of morphological changes in the stressed cells.
Acknowledgement: Part of my doctoral work was supported by a bursary form the Friedrich-Ebert-Stiftung, Bonn, FRG.
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Dr Michael Groß