Pressure-induced conformational changes in an antigen and an antibody and the implications on their use for hyperbaric immunoadsorption

In Situ Monitoring of Protein Unfolding/Structural States under Cold High-Pressure Stress

Biopharmaceutical formulations may be compromised by freezing, which has been attributed to protein conformational changes at a low temperature, and adsorption to ice-liquid interfaces. However, direct measurements of unfolding/conformational changes in sub-0 °C environments are limited because at ambient pressure, freezing of water can occur, which limits the applicability of otherwise commonly used analytical techniques without specifically tailored instrumentation. In this report, small-angle neutron scattering (SANS) and intrinsic fluorescence (FL) were used to provide in situ analysis of protein tertiary structure/folding at temperatures as low as -15 °C utilizing a high-pressure (HP) environment (up to 3 kbar) that prevents water from freezing. The results show that the α-chymotrypsinogen A (aCgn) structure is reasonably maintained under acidic pH (and corresponding pD) for all conditions of pressure and temperature tested. On the other hand, reversible structural changes and formation of oligomeric species were detected near -10 °C via HP-SANS for ovalbumin under neutral pD conditions. This was found to be related to the proximity of the temperature of cold denaturation of ovalbumin (T_CD ∼ -17 °C; calculated via isothermal chemical denaturation and Gibbs-Helmholtz extrapolation) rather than a pressure effect. Significant structural changes were also observed for a monoclonal antibody, anti-streptavidin IgG1 (AS-IgG1), under acidic conditions near -5 °C and a pressure of ∼2 kbar. The conformational perturbation detected for AS-IgG1 is proposed to be consistent with the formation of unfolding intermediates such as molten globule states. Overall, the in situ approaches described here offer a means to characterize the conformational stability of biopharmaceuticals and proteins more generally under cold-temperature stress by the assessment of structural alteration, self-association, and reversibility of each process. This offers an alternative to current ex situ methods that are based on higher temperatures and subsequent extrapolation of the data and interpretations to the cold-temperature regime.

Antibodies under pressure: A Small-Angle X-ray Scattering study of Immunoglobulin G under high hydrostatic pressure

In the present work two subclasses of the human antibody Immunoglobulin G (IgG) have been investigated by Small-Angle X-ray Scattering under high hydrostatic pressures up to 5kbar. It is shown that IgG adopts a symmetric T-shape in solution which differs significantly from available crystal structures. Moreover, high-pressure experiments verify the high stability of the IgG molecule. It is not unfolded by hydrostatic pressures of up to 5kbar but a slight increase of the radius of gyration was observed at elevated pressures.

Conformational study of globulin from rice (Oryza sativa) seeds by Fourier-transform infrared spectroscopy

The conformation of rice globulin (10%, w/v, in deuterated phosphate buffer, pD 7.4) under the influence of pH, chaotropic salts, several protein structure perturbants and heat treatments was studied by Fourier-transform infrared (FTIR) spectroscopy. Rice globulin exhibited seven major bands in the region of 1700-1600 cm-1 and the spectrum suggests high alpha-helical content with large quantities of beta-sheet and beta-turn structures. Highly acidic and alkaline pH conditions induced changes in band intensity attributed to intermolecular beta-sheet structure (1681 and 1619 cm-1). Addition of chaotropic salts led to progressive changes in band intensity, following the lyotropic series of anions, whereas several protein structure perturbants caused shifts in band positions. Heating at increasing temperature led to progressive decreases in alpha-helical content and increases in random coil structures, suggesting protein denaturation. This was accompanied by intensity increases in the intermolecular beta-sheet transitions.

The use of high pressure for separation and production of bioactive molecules

Due to its action on the forces governing inter- and intramolecular interactions, the application of high pressure to biopurification or bio-elaboration of a product are of interest. The two closely thermodynamically related parameters, pressure and temperature, render processes based on their action clean, as no chemical reagents have to be added (and thus further removed) when they are applied. The use of high pressure in the development of desorption methods for the purification of bioactive molecules, particularly in the immunoaffinity field, is reviewed and discussed. Also mentioned is the application of the pressure parameter during the synthesis of a bioreagent. Finally, integrated processes relative to the synthesis and purification of these compounds are proposed.

Fourier-transform infrared spectroscopic study of globulin from Phaseolus angularis (red bean)

The conformation of red bean globulin dispersions (approximately 10% in D2O or deuterated phosphate buffer pD 7.4) under the influence of pH, chaotropic salts, protein structure perturbants, and heating conditions was studied by Fourier-transform infrared (FTIR) spectroscopy. The FTIR spectrum of red bean globulin showed major bands from 1682 to 1637 cm(-1) in the amide I' region, corresponding to the four types of secondary structures, i.e. beta-turns, beta-sheets, alpha-helix and random coils. At extreme pH conditions, there were changes in intensity in bands attributed to beta-sheet (1637 and 1618 cm(-1)) and random coil (1644 cm(-1)) structures, and shifts of these bands to lower or higher wave numbers, indicating changes in protein conformation. Chaotropic salts caused progressive increases in random coil structures and concomitant decreases in beta-sheet bands, following the lyotrophic series of anions. In the presence of sodium dodecyl sulfate and ethylene glycol, pronounced increases in the random coil band were observed, accompanied by slight shifts of the beta-sheet band. Addition of dithiothreitol and N-ethylmaleimide did not cause marked changes in the FTIR spectra. Heating at increasing temperature led to progressive decreases in the intensity of the alpha-helix and beta-sheet bands and increases in random coil band intensity, leveling off at around 60 degrees C. The data suggest that re-organization of protein structure occurred at temperatures well below the denaturation temperature of red bean globulin (86 degrees C) as determined by differential scanning calorimetry. This was accompanied by pronounced increases in the intensity of the two intermolecular beta-sheet bands (1682 and 1619-1620 cm(-1)) associated with the formation of aggregated strands at higher temperatures (80-90 degrees C). Increases in intensity of the aggregation bands were also observed in the heat-induced buffer-soluble and insoluble aggregates.

Effects of high hydrostatic pressures on living cells: a consequence of the properties of macromolecules and macromolecule-associated water

Sixty percent of the Earth's biomass is found in the sea, at depths greater than 1000 m, i.e., at hydrostatic pressures higher than 100 atm. Still more surprising is the fact that living cells can reversibly withstand pressure shifts of 1000 atm. One explanation lies in the properties of cellular water. Water forms a very thin film around macromolecules, with a heterogeneous structure that is an image of the heterogeneity of the macromolecular surface. The density of water in contact with macromolecules reflects the physical properties of their different domains. Therefore, any macromolecular shape variations involving the reorganization of water and concomitant density changes are sensitive to pressure (Le Chatelier's principle). Most of the pressure-induced changes to macromolecules are reversible up to 2000 atm. Both the effects of pressure shifts on living cells and the characteristics of pressure-adapted species are opening new perspectives on fundamental problems such as regulation and adaptation.

Perturbed angular correlation experiments on the pressure-induced structural modification of bovine serum albumin

The hydrodynamic behaviour of the bovine serum albumin (BSA) was studied by means of the Perturbed Angular Correlation (PAC) technique as a function of the hydrostatic pressure (up to 4.1 kbar) applied to the sample. The results have clearly shown that at moderated pressures (around 1.5 kbar) the BSA molecule suffers structural modifications which produces an increase of the molecular volume and the rotational correlation time of the molecule. About the reversibility of the process, our results indicate that the changes are fully irreversible. Our experiments are the first devoted to the study of the high-pressure behaviour of biological molecules using the PAC technique.

Structure of pressure-induced denatured state of human serum albumin: a comparison with the intermediate in urea-induced denaturation

The structure of human serum albumin (HSA) in the pressure-induced denatured state was investigated by fluorescence spectroscopy. HSA undergoes a conformational change in the pressure range from 0.1 MPa to 400 MPa, at 25 degrees C. Several ligands bind to specific sites in HSA, and the fluorescence spectra of these ligands were used to study the conformational state of this protein. The warfarin-binding site (site I) and the dansylsarcosine-binding site (site II), are located in subdomains II and III, respectively. The fluorescence spectra of these probes reflected the structural changes in each of these subdomains. Dansylsarcosine completely dissociated from its binding site in domain III above 300 MPa, but substantial affinity of warfarin remained in this pressure range. Similar results were obtained for the urea-induced denaturation of HSA; although dansylsarcosine completely dissociated at urea concentration above 6 M, warfarin remained bound to site I in domain II at these concentrations. These results suggest that the structure of domain III is unfolded both in the initial stages of both pressure- and urea-induced denaturation of HSA. HSA possesses a single tryptophan residue (Trp-214) in domain II, and fluorescence from this residue reflects structural changes in this domain. In the urea-induced denatured state of HSA, a red-shift in the wavelength of maximum fluorescence occurred over urea concentrations ranging from 4 M to 6 M. This shift indicated that a structural change in domain II occurred simultaneously with the unfolding of domain III in this concentration range. On other hand, the shift in the wavelength of maximum fluorescence of Trp-214 was comparatively small in the pressure range from 0.1 MPa to 400 MPa indicating that the environment of Trp-214 was not affected. These results indicate that preferential unfolding of domain III occurs in the pressure-induced denatured state of HSA.

Pressure-tuning the conformation of bovine pancreatic trypsin inhibitor studied by Fourier-transform infrared spectroscopy

A hydrostatic pressure of 1.5 GPa induces changes in the secondary structure of bovine pancreatic trypsin inhibitor (BPTI) as revealed by the analysis of the amide I' band with Fourier-transform infrared (FTIR) spectroscopy in the diamond anvil cell. The features of the secondary structure remain distinct at high pressure suggesting that the protein does not unfold. The fitted percentages of the secondary structure elements during compression and decompression strongly suggest that the pressure-induced changes are reversible. The pressure-induced changes in the tyrosine side chain band are also reversible. The results demonstrate that the infrared technique explores different aspects of the behaviour of proteins in comparison with two published molecular dynamics studies performed up to 1 GPa [Kitchen, D.B., Reed, L.H. & Levy, R.M.(1992) Biochemistry 31, 10083-10093] and 500 MPa [Brunne, R.M. & van Gunsteren, W.F.(1993) FEBS Lett. 323, 215-217]. A possible explanation for the difference is the time scale of the experiments.

Infrared and circular dichroism spectroscopic characterization of structural differences between beta-lactoglobulin A and B

Structural differences between two genetic variants of bovine beta-lactoglobulins (type A and B) in aqueous solutions were characterized using Fourier transform infrared and circular dichroism spectroscopies. To probe differences in structural dynamics, the effects hydrogen-deuterium exchange were also compared for the two proteins. The infrared spectra recorded in H2O solution for the two proteins were nearly identical in the conformationlly sensitive amide I region. The only exceptions were small differences at the band ascribed to a high-wavenumber beta-sheet component near 1693 cm-1 and the band assigned to turns at 1684 cm-1. In contrast, when the proteins were prepared in D2O solution, marked spectral differences were observed at all regions ascribed to beta-sheet and turn structures. These differences are consistent with the structural differences of the two variants at amino acid residues 64 and 118, which are located at a turn and a beta-sheet structure, respectively, as revealed by X-ray crystallographic studies [Monaco et al. (1987) J. Mol. Biol. 197, 695-706]. The circular dichroism spectra for the two proteins were essentially identical, both before and after hydrogen-deuterium exchange. Therefore, hydrogen-deuterium exchange did not alter the proteins' secondary structure. The enhancement of the amide I spectral difference upon hydrogen-deuterium exchange was ascribed to the differences in the structural mobility of the two proteins. Since the rate of exchange was greater for variant A, it was concluded that this variant has greater structural mobility than variant B. These findings indicate that the combination of infrared spectroscopy and hydrogen-deuterium exchange has great potential in characterization of even subtle structural differences in proteins induced by naturally occurring point mutations and/or site-directed mutagenesis.

Pressure-induced inactivation of E. coli beta-galactosidase: influence of pH and temperature

In order to assess the feasibility of a high-pressure immunodesorption process using a beta-galactosidase-anti-beta-galactosidase complex as a model, the influence of high hydrostatic pressure on the activation of E. coli beta-galactosidase has been investigated. The irreversible activity loss of beta-galactosidase was studied as a function of pH and temperature for pressures comprised between atmospheric pressure and 500 megapascal (MPa; 1 MPa = 10 bar). This enabled us to establish a practical pressure-temperature diagram of stability for this enzyme. The stability domains determined thus appeared to be strongly dependent on the pH under atmospheric pressure of phosphate buffer employed for pressurisation. Therefore, to interpret meaningfully this result, the influence of pressure on the pH-activity curve of beta-galactosidase was investigated by using a high-pressure stopped-flow device. It appeared that the pH-activity curve of this enzyme was also reversibly affected by pressures lower than 150 MPa. An interpretation of these results in relation to the high-pressure induced changes of ionisation constants is proposed. For our practical purpose, the implications for the elaboration of a high-pressure immunodesorption process using beta-galactosidase as a tag, are discussed.

Pressure-induced dissociation of fluorescein from the anti-fluorescein single-chain antibody 4-4-20

Hydrostatic pressure was used to dissociate fluorescein (Fl) from the high-affinity anti-Fl single-chain antibody 4-4-20 (SCA 4-4-20). Fl dissociation was monitored by measuring (1) the shift in the Fl absorption peak, (2) the recovery in Fl fluorescence intensity, which is quenched upon SCA binding, or (3) the decrease in Fl fluorescence polarization. Pressure effects were studied at two different Fl:SCA 4-4-20 molar ratios: 1:1, at which Fl fluorescence quenching was ca. 35% at atmospheric pressure, and 1:5, at which quenching reached 95-97% under the same conditions. In both cases, pressure-induced dissociation was favored by concomitant dilution of protein and ligand. Dissociation constants (KD) at each pressure were calculated on the basis of measurements of Fl fluorescence polarization under pressure. The dependence of KD, and consequently of delta G of dissociation, on pressure permitted calculation of the magnitude of the standard volume change (delta V) involved in the dissociation process. According to this study, delta V of dissociation for the Fl-SCA complex is -50 mL/mol, which corresponds to a 10-times higher value than that found for dissociation of Fl from the intact IgG mAb 4-4-20 [Herron, J. N., Kranz, D. M., Jameson, D. M., & Voss, E. W., Jr. (1986) Biochemistry 25, 4602-4609]. This difference is explained in terms of a higher overall flexibility of unliganded SCA and of a less stable binding site in SCA relative to mAb.(ABSTRACT TRUNCATED AT 250 WORDS)