High-performance liquid chromatography of amino acids, peptides and proteins. XCI. The influence of temperature on the chromatographic behaviour of peptides related to human growth hormone

Effects of oligopeptide's conformational changes on its adsorption

We report the effects of peptide adsorption to cross-linked polymers (adsorbents) by its conformational changes. Two adsorbents, APhe and ALeu, were prepared and expected to show high affinity to the oligopeptide VW-8 (NH(2)-Val-Val-Arg-Gly-Cys-Thr-Trp-Trp-COOH) according to our previous studies. These absorbents bared the residues of phenylalanine and leucine, respectively, and carried both hydrophobic and electrical groups. The adsorbent AAsp, which carried only the electrostatic groups, was also prepared as a reference. Both APhe and ALeu were found to exhibit higher VW-8 capacity than AAsp, in which APhe showed the highest VW-8 capacity (13.6 mg/g). The VW-8 adsorption to ALeu and APhe was analyzed using a variety of techniques, including the surface plasmon resonance (SPR) technology, nuclear magnetic resonance (NMR) spectra and isothermal titration calorimetry (ITC). The comprehensive experimental data together indicated that APhe could induce a conformational change of VW-8 from a random-coil to a β-strand structure due to its ability to provide the strong ring stacking and electrostatic interactions, which is believed to be responsible for its highest adsorption affinity (K(a)=2.59×10(7) M(-1)). In contrast, the hydrophobic interactions provided by ALeu were not strong enough to induce a VW-8 conformational change to a regular structure, and therefore it exhibited a relatively lower affinity to VW-8 (K(a)=6.23×10(5) M(-1)). The results presented in this work showed that peptide adsorption can be influenced by its conformational changes induced by suitable adsorbents via strong non-covalent interactions.

Temperature profiling of polypeptides in reversed-phase liquid chromatography. II. Monitoring of folding and stability of two-stranded alpha-helical coiled-coils

The present study extends the utility of reversed-phase high-performance liquid chromatography (RP-HPLC) to monitor folding and stability of de novo designed synthetic two-stranded alpha-helical coiled-coils. Thus, we have compared the effect of temperature on the RP-HPLC retention behaviour of both oxidized (two identical five-heptad alpha-helical peptides linked by a disulfide bridge) and reduced coiled-coil analogues with various amino acids substituted into the hydrophobic core of the coiled-coil. We were able to correlate the RP-HPLC retention behaviour of the oxidized analogues over the temperature range of 10 to 80 degrees C with the stability of the analogues as determined by conventional thermal and chemical denaturation approaches. In addition, the contribution of a disulfide bridge to coiled-coil stability was highlighted by comparing the elution behaviour of the oxidized and reduced analogues. Overall, we demonstrate the excellent potential of "temperature profiling" by RP-HPLC to monitor differences in oligomerization state and protein stability.

Temperature profiling of polypeptides in reversed-phase liquid chromatography

The present study sets out to extend the utility of reversed-phase liquid chromatography (RP-HPLC) by demonstrating its ability to monitor dimerization and unfolding of de novo designed synthetic amphipathic alpha-helical peptides on stationary phases of varying hydrophobicity. Thus, we have compared the effect of temperature (5-80 degrees C) on the RP-HPLC (C8 or cyano columns) elution behaviour of mixtures of peptides encompassing amphipathic alpha-helical structure, amphipathic alpha-helical structure with L- or D-substitutions or non-amphipathic alpha-helical structure. By comparing the retention behaviour of the helical peptides to a peptide of negligible secondary structure (a random coil), we rationalize that "temperature profiling" by RP-HPLC can monitor association of peptide molecules, either through oligomerization or aggregation, or monitor unfolding of alpha-helical peptides with increasing temperature. We believe that the conformation-dependent response of peptides to RP-HPLC under changing temperature has implications both for general analysis and purification of peptides but also for the de novo design of peptides and proteins.

Protein unfolding during reversed-phase chromatography: I. Effect of surface properties and duration of adsorption

Residue-level features of bovine pancreatic trypsin inhibitor (BPTI) unfolding on reversed-phase chromatography (RPC) surfaces were investigated using hydrogen-deuterium exchange labeling and NMR. A set of silica-based RPC surfaces was used to examine the influence of alkyl chain length and media pore size on adsorbed BPTI conformation. In all cases there was substantial unfolding in the adsorbed state; however, residual protection from exchange was consistently observed. Particle pore size did not influence conformation substantially for C4-alkyl modified silica; however, 120 A pore C18 media produced more hydrogen exchange than any other surface examined. In this case, the radius of curvature inside the pore approaches the size of the BPTI molecule. Generally, the pattern of hydrogen exchange protection was uniform; however, the beta-sheet region was selectively protected on the large-pore C18 media. The beta-sheet region forms a hydrophobic core that forms early when BPTI folds in solution. This suggests that partially unfolded states possessing a native-like structure play an important role in adsorption and elution in RPC. Finally, increased contact time with the surface before elution fostered unfolding and altered chromatographic behavior considerably.

Protein unfolding during reversed-phase chromatography: II. Role of salt type and ionic strength

While reversed-phase chromatography (RPC) may be a powerful method for purification of proteins at the analytical scale, both preparative and analytical applications have been hindered by the complex chromatographic behavior of proteins compared to small molecules. Further, preparative applications have been limited because of poor yields caused by the denaturing conditions involved. One means for modulating both the stability and chromatographic behavior of proteins is through the use of added salt. In this investigation, we show how salt type and ionic strength affect protein conformation on RPC surfaces. Exposure of amide groups of adsorbed BPTI was monitored using nuclear magnetic resonance (NMR) spectroscopy and hydrogen-deuterium isotope exchange. Sodium chloride, sodium acetate, and ammonium sulfate were studied at ionic strengths up to I = 0.375, with adsorption hold times being 5 min and 2 h. We found that increasing ionic strength decreased exposure of the exchange reporter groups in essentially all cases. However, even at the same ionic strength the level and distribution of residue protection varied with salt type and hold time. NaCl does not protect certain reporter groups at all, while those that it does protect to some degree at short hold times can exchange slightly more at longer times. The pattern and level of protection for NaAc at short times is similar to that for NaCl, but at longer times more uniform protection is seen as the reporter groups completely exposed at short times become more protected. For (NH(4))(2)SO(4) the pattern of protection at short hold time is similar to those of the other salts, although it protects all groups much more. This would be expected from the Hofmeister series. However, at longer times the level of protection with (NH(4))(2)SO(4) decreases below that of the other salts, while it uniquely protects all groups to nearly the same level. Such subtle variations in the protein structure would not have been detected without the measurements and analysis used here. Chromatographic retention times and peak shapes were obtained for the above systems. Variations of behavior were seen that could not be correlated with any of the above protection patterns and levels or even with heuristics such as the Hofmeister series. This suggests further conformational changes upon elution may be critical to the retention process. However, an excellent correlation was found between peak width at half-height and the average degree of unfolding, as indicated by the average level of isotopic exchange. Thus, while further studies are needed to definitively determine the connection between protein unfolding and retention, use of this correlation may improve designing and screening for chromatographic conditions that minimize protein unfolding.

Conformational analysis of neuropeptide Y-[18-36] analogs in hydrophobic environments

The interactive and conformational behavior of a series of neuropeptide Y-[18-36] (NPY-[18-36]) analogs in hydrophobic environments have been investigated using reversed-phase high-performance liquid chromatography (RP-HPLC) and circular dichroism (CD) spectroscopy. The peptides studied comprised a series of 16 analogs of NPY-[18-36], each containing a single D-amino acid substitution. The influence of these single L-->D substitutions on the alpha-helical conformation of the NPY-[18-36] analogs in different solvent environments was determined by CD spectroscopy. Retention parameters related to the hydrophobic contact area and the affinity of interaction were determined with an n-octadecyl (C18) adsorbent. Structural transitions for all peptides were manifested as significant changes in the hydrophobic binding domain and surface affinity between 4 degrees C and 37 degrees C. The results indicated that the central region of NPY-[18-36] (residues 23-33) is important for maintenance of the alpha-helical conformation. Moreover, L-->D amino acid residue substitutions within the N- and C-terminal regions, as well as Asn29 and Leu30, do not appear to affect the secondary structure of the peptide. These studies demonstrate that RP-HPLC provides a powerful adjunct for investigations into the induction of stabilized secondary structure in peptides upon their interaction with hydrophobic surfaces.

Conformational effects in reversed-phase high-performance liquid chromatography of polypeptides. I. Resolution of insulin variants

In order to further characterise the role of conformation in the retention behaviour of polypeptides and proteins in reversed-phase high-performance liquid chromatography (RP-HPLC), the chromatographic properties of four different insulins have been studied as a function of temperature (over the range 5-85 degrees C) and column residence time (over the range 10-60 min). The role of the ligand structure was also investigated by comparing results obtained with a n-octadecyl (C18) and a n-butyl (C4) ligand immobilised to the same porous silica. Comparative structure-retention-stability relationships were determined from an examination of the influence of temperature on a number of chromatographic parameters including the chromatographic contact area, the affinity constant and the experimental band width. The results demonstrated that variations in temperature can be used to affect significant changes in selectivity between the different insulins despite their very high degree of sequence homology. These observations have permitted specific amino acid residues, and in particular those residues encompassing the region A8-A10, to be proposed to be directly involved in the chromatographic contact area of the insulin molecules. Overall, the analysis of the changes in various chromatographic parameters in response to variation of the amino acid sequence, temperature and other experimental parameters provides a powerful tool to elucidate the structural basis for the interfacial stability and the role of conformation on the retention behaviour of polypeptides and proteins in RP-HPLC.

Study of conformational effects of recombinant interferon gamma adsorbed on a non-porous reversed-phase silica support

Reversed-phase chromatography is a powerful method for separating recombinant interferon gamma and one of its analogues differing only by a single amino acid residue. Structural differences of the proteins explain this separation ability as demonstrated from adsorption studies on a non-porous reversed-phase support. To reveal the structural differences occurring in the adsorbed state, two different and independent methods were employed. The variation of the retention with the slope of the linear gradient gave information about the molecular contact area of the protein with the support. For different experimental conditions, these data were correlated with the adsorbent capacities measured on an n-octadecyl-modified non-porous silica support. These supports are useful for these types of experiments because the protein is adsorbed exclusively at the external surface of the beads. Moreover, a small amount of protein is necessary to saturate the column, owing to its low capacity.

Validation and optimization of a polymer system for potential use as a controlled drug-delivery system

A room temperature polymerizing system consisting of polyethylmethacrylate (PEM) and tetrahydrofurfuryl methacrylate (THFMA) monomer was validated for use as a drug-delivery system. The effect of gelling PEM/THFMA copolymers with a more hydrophilic monomer, hydroxyethyl methacrylate (HEMA), was also investigated. The release of growth hormone (GH) and bovine serum albumin (BSA) protein from this polymer has been studied. The polymer has the advantage of high water absorption and low shrinkage properties. Changes in release profiles have been studied by introducing structural differences in the polymer by changing the mixing technique. The stability and bioactivity of the GH incorporated have been examined at various temperatures. To optimize release profiles further, the possibility of attaining a more sustained and controllable release by varying the ratios of polymer used has also been investigated.

Anion-exchange chromatographic behavior of recombinant rat cytochrome b5. Thermodynamic driving forces and temperature dependence of the stoichiometric displacement parameter Z

The HPLC anion-exchange isocratic retention behavior of the recombinant soluble core of wild type rat cytochrome b5 on Mono Q HR 5/5 was investigated as a function of temperature and sodium chloride concentration at fixed eluent flow-rates. Retention was measured over a range of eluent flow-rates at a specified temperature to determine if true adsorption equilibrium could be approximated by the HPLC method. Apparent Van 't Hoff enthalpies of adsorption obtained from the HPLC retention data were positive, indicating an entropically driven spontaneous adsorption process, and were found to decline with increasing ionic strength. The retention results were interpreted in terms of the stoichiometric displacement model to obtain the apparent number of binding sites in the contact region, Z, as a function of temperature and of protein concentration. Z was found to depend significantly on temperature, even under conditions of nearly complete protein recovery, but did not depend on protein concentration at the low loadings studied.

High-performance liquid chromatography of amino acids, peptides and proteins. CXXII. Application of experimentally derived retention coefficients to the prediction of peptide retention times: studies with myohemerythrin

Amino acid retention coefficients were derived from the experimental retention data of 118 overlapping peptide heptamers related to the primary amino acid sequence of myohemerythrin. Individual retention coefficient values for each amino acid were derived by a multiple linear regression matrix approach. Retention data were derived for five different experimental conditions including different organic modifiers (acetonitrile, methanol or 2-propanol), different mobile phase additives (trifluoroacetic acid or potassium phosphate) and different silica-based stationary phase ligands (octadecyl or phenyl groups). A high degree of correlation was observed between these experimentally derived amino acid coefficients (EXP) and the coefficients (LIT) which we recently reported derived from the retention data of over 2000 peptides [M. C. J. Wilce et al., J. Chromatogr., 536 (1991) 165 and 548 (1991) 105]. These results demonstrated that the LIT and EXP coefficients can be used for the prediction of the retention of any peptide set. The effect of peptide length was also further investigated and the correlation results demonstrated the importance of peptide flexibility on the final value of the amino acid coefficient.

Support matrix effects in the reversed-phase thin-layer chromatography of some peptides

The retentions of 28 peptides in reversed-phase thin-layer chromatography (RPTLC) were determined on cellulose and on impregnated cellulose and alumina layers with 1-propanol as the organic component of the mobile phase. Each peptide showed a support matrix effect: their RM values first decreased to a minimum, then increased with increasing 1-propanol concentration. On cellulose layers only the increasing phase was observed. The retention behaviour of peptides was adequately described with a quadratic or linear function, but the slope value of the linear function had a positive value. The results demonstrate that the support matrix effect can be observed on non-silica supports and it may occur in reversed-phase chromatography in the case of polar solutes and supports with free adsorptive centres on their surfaces. Both the intercept and slope values of the function are needed to describe the lipophilicity of peptides, but the correlation is not strong enough for the determination of the lipophilicity of peptides by RPTLC. Principal component analysis showed that the peptides form distinct clusters on the basis of their retention characteristics: peptides containing a basic amino acid, peptides with a ring structure in the amino acid side-chain and peptides containing uncharged amino acids.

High-performance liquid chromatography of amino acids, peptides and proteins. CXV. Thermodynamic behaviour of peptides in reversed-phase chromatography

The thermodynamic behaviour of three peptides, bombesin, beta-endorphin and glucagon, was studied under reversed-phase high-performance liquid chromatographic conditions. Experimental data related to the interactive surface contact area (S values) and solute affinity (log k0) were derived over a range of temperatures between 5 and 85 degrees C. These experimental conditions allowed changes in the secondary structure of the solute to be monitored. The influence of the nature of the stationary phase ligand on the relative conformational stability of the three peptides was analysed by acquiring data with n-octadecyl silica (C18) and n-butyl silica (C4) sorbents. Values for the relative changes in entropy and enthalpy associated with the interactive process were also determined. The results provide further insight into the factors involved with the stabilization of secondary structure and the mechanism of the interaction of peptides with hydrophobic surfaces.

Determination of the lipophilicity of some peptides. Effect of surface pH of silica

The lipophilicities of 22 peptides were determined by reversed-phase thin-layer chromatography using methanol as organic modifier in the concentration range 0-90 vol.-% on silica supports with surface pH values of 2.0,4.5,6.0,7.5 and 9.0. Only one of the 22 peptides (Trp-Ala-Ile) followed the general rule, i.e., its RM value decreased linearly with increasing proportion of organic modifier over the whole concentration range. Most peptides exhibited typical silanophilic retention behaviour, the RM value decreasing with increasing organic phase concentration in the lower concentration range and then increasing with further increase in the proportion of organic modifier. In some instances the lipophilicity increased linearly with increasing proportion of methanol. The silanophilic effect depended not only on the structure of the peptide, but also on the surface pH of the silica support. The retention behaviour of peptides can be well described by a polynomial function, the linear and quadratic forms of methanol concentration and surface pH being the independent variables. Principal component analysis showed that the presence of a ring structure in the peptides has the greatest impact on their retention behaviour, the overall polarity (basic, neutral or acidic) being of secondary importance. The number of amino acids in the peptide has a negligible effect on the chromatographic behaviour.

High-performance liquid chromatography of amino acids, peptides and proteins. XCIII. Comparison of methods for the purification of mouse monoclonal immunoglobulin M autoantibodies

A comparison of methods for the purification of naturally occurring mouse monoclonal autoantibodies, of the immunoglobulin M (IgM) isotype, has been performed to determine the optimal strategies for the isolation of IgM from ascites fluid and in vitro tissue culture hybridoma supernatants. In order to quantify each purification procedure, the concentration of IgM in eluted fractions was determined by using a double-sandwich mu-chain-specific anti-IgM enzyme-linked immunosorbent assay, and the purity of the IgM was determined by a bicinchoninic acid-based protein assay and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The most efficient single-step purification was based on size-exclusion chromatography on high-resolution Superose 6 HR 10/30 fast protein liquid chromatography (FPLC) columns. This procedure resulted in recoveries of monoclonal IgMs of ca. 71-86% with purities between 68 and 86%. Single-step chromatography of monoclonal IgM, on Superose 6 FPLC columns resulted in a 21-fold purification of IgM, prepared by the in vitro culture of hybridoma cells in dialysis membrane. Size-exclusion chromatography, performed with Sephacryl S-300 columns, resulted in reduced resolution of monoclonal IgM, with yields of ca. 57-80% and purity of ca. 42-58% compared with the high-resolution Superose 6 FPLC columns. "Non-ideal" size-exclusion chromatography on Superose 6 FPLC columns resulted in selective retention of monoclonal IgMs and elution of IgM with high-ionic-strength buffers in the trailing peak. Recovery of IgM with this strategy was high (ca. 82-92%) but the purity was not comparable to the single-step fractionation of IgM on Superose 6 FPLC columns. Single-step anion- and cation-exchange and mixed-mode hydroxyapatite chromatography resulted in only partial purification of monoclonal IgM with the applied procedures. With these latter separation techniques, monoclonal IgM was eluted with a variety of other ascites fluid or supernatant proteins, including those with apparent molecular weights identical to those of mouse IgG and albumin. Sequential purification of monoclonal IgMs by Mono Q anion exchange, followed by Superose 6 FPLC columns, resulted in a 2- to 3-fold purification of IgM but did not separate IgM from high-molecular-weight contaminants with apparent molecular weights similar to those of alpha 2-macroglobulin and IgG. Enrichment of monoclonal IgM from ascites fluid by ammonium sulphate precipitation revealed increasing IgM recovery with increasing ammonium sulphate final concentrations up to 60%.(ABSTRACT TRUNCATED AT 400 WORDS)

High-performance liquid chromatography of amino acids, peptides and proteins. XCII Thermodynamic and kinetic investigations on rigid and soft affinity gels with varying particle and pore sizes

In these investigations Cibacron Blue F3GA was immobilized on soft gels, porous silicas, and non-porous glass beads. Hen egg white lysozyme, human serum albumin and yeast alcohol dehydrogenase were used as adsorbates with the dye-affinity sorbents. Batch experiments with continuous monitoring of protein concentration were employed to evaluate thermodynamic and kinetic behaviour of these proteins in finite bath systems. The observed adsorption kinetic rates of interaction of the above proteins with each of the dye-affinity sorbents were found to decrease with increasing protein molecular weight. Equilibration times, in the batch experimental mode, of the adsorption of lysozyme on the dye-affinity sorbents varied from 20 s for the non-porous glass beads with a size range of 20-40 microns to more than 60 min in the case of a porous sorbent with a particle diameter of 100-300 microns and 60 nm pore size. Furthermore, equilibration times, which represent the overall adsorption rates incorporating all the non-equilibrium effects, increased with all affinity systems when adsorption took place in the non-linear portion of the isotherm. The most dramatic increase was observed when sorbents with relatively high protein size to pore size ratios, lambda, were employed.