Pressure-induced molten globule state of cholinesterase

The denaturing effect of pressure on the structure of human butyrylcholinesterase was examined by gel electrophoresis under pressure and by 8-anilino-1-naphthalene sulfonate (ANS) binding. It was found that the fluorescence intensity of bound ANS is increased by pressure between 0.5 and 1.5 kbar and that the hydrodynamic volume of the enzyme swells when pressures around 1.5 kbar are applied. These findings indicate that pressure denaturation of butyrylcholinesterase is a multi-step process and that the observed transient pressure-denatured states have characteristics of molten globules.     

Diurnal changes in xylem pressure and mesophyll cell turgor pressure of the lianaTetrastigma voinierianum — the role of cell turgor in long-distance water transport: a comment

Summary The calculation of absolute-pressure values on the basis of measurements with differential-gauge pressure sensors, as described by Thürmer et al. (Protoplasma 206: 152–162, 1999), leads to discrepancies with the definition of absolute pressure when negative values are reached. From previous experiments with the xylem pressure probe we can conclude that the recorded pressure signal belongs not only to the xylem pressure, as stated by the authors, but also to the capillary pressure.     

Variability of pressure adaptation in deep sea bacteria

Isolations of pressure-adapted deep sea bacteria from depths of 1,400 to 5,100 m resulted in a variety of psychrophilic barotolerant and barophilic strains. Growth rates determined at different pressures indicated a gradual transition between the two types of pressure-adapted isolates. The presence of barotolerant bacteria in deep water, sustained by sinking particulate matter, causes the nonbarophilic response of natural populations, i.e., increased growth after decompression. With increasing pressure-adaptation in barophilic isolates the maximum growth rates at optimum pressures decrease. Thus, the observed general slow-down of microbial activity in the deep sea takes effect regardless of the common occurrence of psychrophilic and barophilic bacteria. The highest degree of barophilism was observed in isolates from nutrient-rich habitats such as intestinal tracts of deep sea animals or decaying carcasses. Detailed studies with an isolate, growing barophilically on a complex as well as a single-carbon-source medium, showed that (1) culturing at pressures lower than optimal for growth resulted in the formation of cell filaments, (2) growth was unaffected by repeated compression/decompression cycles and (3) no perceptible differences in the distribution of radiolabeled carbon from an amino acid mixture occurred in cells grown at, below and above the pressure optimal for growth.Dedicated to Professor Dr. Hans G. Schlegel on the occasion of his 60th birthday in recognition of his broad microbiological interests and in special appreciation of his lasting support for the Marine Microbiology Course at the Stazione Zoologica (Naples, Italy) now for almost 25 years Non-standard abbreviations. The traditional use of atm as a unit of pressure (=10 m of water column, =1.013 bar, =101.3 kN/m²) is retained here in view of the important relation between water depth and hydrostatic pressure in the present study. Due to the compression of seawater and the geographic variability of gravity, there is a progressive deviation of the actual pressure with depth amounting to +4.9 atm at 5,000 m and a latitude of 30°. EPC, cell counts obtained by epifluorescence microscopy. PY, peptone yeast extract medium     

Pressure-induced change in proteins studied through chemical modifications

Pressure-induced change of two bovine proteins, α-lactalbumin (LA) and β-lactoglobulin (LG), was investigated at neutral pH by means of fluorescence and CD spectroscopy. The rate and the extent of modification was considerably increased by applying high pressure during the dansylation reaction of LG, while those for LA were only moderately affected. This difference was accounted for by the structural deformation of these proteins under high pressure. The fluorescence spectrum of these proteins measured under elevated pressure, as well as their fluorescence and CD spectra after the pressure release, indicated different responses towards pressure. The structural change of LA was practically reversible up to 400 MPa, whereas that of LG lost reversibility at 150 MPa or lower. Fluorescent measurement of dansylated (prepared at atmospheric pressure) proteins, especially the energy transfer from the intrinsic Trp residue to the dansyl group, showed that the protein structure was deformed by pressure and that the energy transfer facility of the two proteins was differently affected by high pressure, probably reflecting the degree of compactness of their pressure-perturbed structures     

Pressure-induced helix–coil transition of DNA copolymers is linked to water activity

We have investigated the effect of reduced water activity on the pressure-stability of double-stranded DNA polymers, poly[d(A-T)] and poly[d(I-C)]. Water activity was modulated by the addition of ethylene glycol and glycerol. The ionic strength of the medium was such that pressure had a destabilising effect on the polymers in the absence of cosolvents. The molar volume change of the heat-induced helix to coil transition (ΔV_T) becomes more positive as the activity of water was reduced, suggesting that the pressure-induced denaturation of DNA polymers would not occur at very low water activity. This would imply that water plays a crucial role in the pressure denaturation of DNA, much like that in pressure denaturation of proteins where the driving force of the process is the penetration of water molecules into the protein core [Hummer et al., Proc Natl Acad Sci USA 1998, 95, 1552–1555].     

Activation volumes for horseradish peroxidase compound ii reactions

The activation volumes for the reactions of horseradish peroxidase compound II with L-tyrosine. 3-iodo-L-tyrosine. p-aminobenzoic acid and ferrocyanide were determined by using a high-pressure stopped-flow technique at 25°C and pH 7. For the tyrosines, the solvent electrostriction accompanying substrate ionization and H⁺ transfer from the substituted phenol to a basic group of the enzyme can account for the observed negative activation volumes. For p-aminobenzoic acid a simple electron transfer without H⁺ transfer appears to occur. The positive activation volume for ferrocyanide may be explained in terms of electron transfer associated with a large change in electrostriction of the inorganic redox couple.     

Diurnal changes in xylem pressure and mesophyll cell turgor pressure of the lianaTetrastigma voinierianum — the role of cell turgor in long-distance water transport: a reply

Summary From equilibrium thermodynamics an equation is given to show that in a liquid negative pressures (tensions) are physical reality and may reliably be recorded from any point of the aqueous phase within the xylem conduit by the xylem pressure probe introduced by Balling et al. (Naturwissenschaften 75: 409–411, 1988).     

Cryo-EM Structure of the Full-length hnRNPA1 Amyloid Fibril

Heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) is a multifunctional RNA-binding protein that is associated with neurodegenerative diseases, such as amyotrophic lateral sclerosis and multisystem proteinopathy. In this study, we have used cryo-electron microscopy to investigate the three-dimensional structure of amyloid fibrils from full-length hnRNPA1 protein. We find that the fibril core is formed by a 45-residue segment of the prion-like low-complexity domain of the protein, whereas the remaining parts of the protein (275 residues) form a fuzzy coat around the fibril core. The fibril consists of two fibril protein stacks that are arranged into a pseudo-2₁ screw symmetry. The ordered core harbors several of the positions that are known to be affected by disease-associated mutations, but does not encompass the most aggregation-prone segments of the protein. These data indicate that the structures of amyloid fibrils from full-length proteins may be more complex than anticipated by current theories on protein misfolding.