Reversed-phase high-performance liquid chromatography of virus proteins and other large hydrophobic proteins in formic acid containing solvents

Preventing N- and O-formylation of proteins when incubated in concentrated formic acid

Concentrated formic acid is among the most effective solvents for protein solubilization. Unfortunately, this acid also presents a risk of inducing chemical modifications thereby limiting its use in proteomics. Previous reports have supported the esterification of serine and threonine residues (O-formylation) for peptides incubated in formic acid. However as shown here, exposure of histone H4 to 80% formic (1 h, 20(o) C) induces N-formylation of two independent lysine residues. Furthermore, incubating a mixture of Escherichia coli proteins in formic acid demonstrates a clear preference toward lysine modification over reactions at serine/threonine. N-formylation accounts for 84% of the 225 uniquely identified formylation sites. To prevent formylation, we provide a detailed investigation of reaction conditions (temperature, time, acid concentration) that define the parameters permitting the use of concentrated formic acid in a proteomics workflow for MS characterization. Proteins can be maintained in 80% formic acid for extended periods (24 h) without inducing modification, so long as the temperature is maintained at or below -20(o) C.

Downstream processing and chromatography based analytical methods for production of vaccines, gene therapy vectors, and bacteriophages

Downstream processing of nanoplexes (viruses, virus-like particles, bacteriophages) is characterized by complexity of the starting material, number of purification methods to choose from, regulations that are setting the frame for the final product and analytical methods for upstream and downstream monitoring. This review gives an overview on the nanoplex downstream challenges and chromatography based analytical methods for efficient monitoring of the nanoplex production.

Development and application of a reversed-phase high-performance liquid chromatographic method for quantitation and characterization of a Chikungunya virus-like particle vaccine

To effectively support the development of a Chikungunya (CHIKV) virus-like particle (VLP) vaccine, a sensitive and robust high-performance liquid chromatography (HPLC) method that can quantitate CHIKV VLPs and monitor product purity throughout the manufacturing process is needed. We developed a sensitive reversed-phase HPLC (RP-HPLC) method that separates capsid, E1, and E2 proteins in CHIKV VLP vaccine with good resolution. Each protein component was verified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry (MS). The post-translational modifications on the viral glycoproteins E1 and E2 were further identified by intact protein mass measurements with liquid chromatography-mass spectrometry (LC-MS). The RP-HPLC method has a linear range of 0.51-12 μg protein, an accuracy of 96-106% and a precision of 12% RSD, suitable for vaccine product release testing. In addition, we demonstrated that the RP-HPLC method is useful for characterizing viral glycoprotein post-translational modifications, monitoring product purity during process development and assessing product stability during formulation development.

Synthesis, purification, and characterization of single helix membrane peptides and proteins for NMR spectroscopy

Membrane proteins function as receptors, channels, transporters, and enzymes. These proteins are generally difficult to express and purify in a functional form due to the hydrophobic nature of their membrane spanning sequences. Studies on membrane proteins with a single membrane spanning helix have been particularly challenging. Single-pass membrane proteins will often form dimers or higher order oligomers in cell membranes as a result of sequence motifs that mediate specific transmembrane helix interactions. Understanding the structural basis for helix association provides insights into how these proteins function. Nevertheless, nonspecific association or aggregation of hydrophobic membrane spanning sequences can occur when isolated transmembrane domains are reconstituted into membrane bilayers or solubilized into detergent micelles for structural studies by solid-state or solution NMR spectroscopy. Here, we outline the methods used to synthesize, purify, and characterize single transmembrane segments for structural studies. Two synthetic strategies are discussed. The first strategy is to express hydrophobic peptides as protein chimera attached to the maltose binding protein. The second strategy is by direct chemical synthesis. Purification is carried out by several complementary chromatography methods. The peptides are solubilized in detergent for solution NMR studies or reconstituted into model membranes for solid-state NMR studies. We describe the methods used to characterize the reconstitution of these systems prior to NMR structural studies to establish if there is nonspecific aggregation.

Chromatographic benefits of elevated temperature for the proteomic analysis of membrane proteins

Integral membrane proteins (IMPs) perform crucial cellular functions and are the primary targets for most pharmaceutical agents. However, the hydrophobic nature of their membrane-embedded domains and their intimate association with lipids make them difficult to handle. Numerous proteomic platforms that include LC separations have been reported for the high-throughput profiling of complex protein samples. However, there are still many challenges to overcome for proteomic analyses of IMPs, especially as compared to their soluble counterparts. In particular, considerations for the technical challenges associated with chromatographic separations are just beginning to be investigated. Here, we review the benefits of using elevated temperatures during LC for the proteomic analysis of complex membrane protein samples.

Matrix-Assisted Laser Desorption/Ionization-Mass Spectrometry of Hydrophobic Proteins in Mixtures Using Formic Acid, Perfluorooctanoic Acid, and Sorbitol

Three MALDI-MS sample/matrix preparation approaches were evaluated for their ability to enhance hydrophobic protein detection from complex mixtures: (1) formic acid-based formulations, (2) perfluorooctanoic acid (PFOA) surfactant addition, and (3) sorbitol addition. While MALDI-MS of Escherichia coli cells desorbed from a standard sinapinic acid matrix displayed 94 (M + H)+ ions, 119 were observed from a formic acid-based matrix with no more than 10 common to both. Formic acid matrix revealed many lipoproteins and an 8282 m/z ion proposed to be the abundant, water-insoluble ATPase proteolipid. Among the formic acid-based cocktails examined, the slowest rate of serine/threonine formylation was found for 50% H2O/33% 2-propanol/17% formic acid. Faster formylation was observed from cocktails containing more formic acid and from mixtures including CH3CN. Sinapinic, ferulic, DHB, 4-hydroxybenzylidene malononitrile, and 2-mercaptobenzothiazole matrixes performed well in formic acid formulations. Dramatic differences in mixture spectra were also observed from PFOA/sinapinic acid, at detergent concentrations exceeding the critical micelle concentration, although these matrix cocktails proved difficult to crystallize. E. coli ions observed from these matrix conditions are listed in Tables S-1 and S-3 (Supporting Information). Similar complementarity was observed for M. acetivorans whole-cell mixtures. Including sorbitol in the sinapinic acid matrix was found to promote homogeneous crystallization and to enhance medium and higher m/z ion detection from dilute E. coli cellular mixtures.

High recovery HPLC separation of lipid rafts for membrane proteome analysis

Proteomic analysis of complex samples can be facilitated by protein fractionation prior to enzymatic or chemical fragmentation combined with MS-based identification of peptides. Although aqueous soluble protein fractionation by liquid chromatography is relatively straightforward, membrane protein separations have a variety of technical challenges. Reversed-phase high performance liquid chromatography (RP-HPLC) separations of membrane proteins often exhibit poor recovery and bandwidths, and generally require extensive pretreatment to remove lipids and other membrane components. Human brain tissue lipid raft protein preparations have been used as a model system to develop RP-HPLC conditions that are effective for protein fractionation, and are compatible with downstream proteomic analytical workflows. By the use of an appropriate RP column material and operational conditions, human brain membrane raft proteins were successfully resolved by RP-HPLC and some of the protein components, including specific integral membrane proteins, identified by downstream SDS-PAGE combined with in-gel digestion, or in-solution digestion and LC-MS/MS analysis of tryptic fragments. Using the described method, total protein recovery was high, and the repeatability of the separation maintained after repeated injections of membrane raft preparations.

Synthesis of a membrane protein with two transmembrane regions

A membrane protein with two transmembrane domains was synthesized by means of the thioester method. The F1F0 ATP synthase subunit c (Sub.c), which consists of 79 amino acid residues (MW 8257), was chosen as a target. For synthetic purposes, two building blocks, Boc-[Lys34(Boc)]-Sub.c(1-38)-SCH2CH2CO-Ala and Sub.c(39-79), were synthesized via solid-phase methods using Boc chemistry. RP-HPLC purification conditions for the transmembrane peptide were examined. As a result, a combination of a mixture of formic acid, 1-propanol and water with a phenyl column was found to be useful for separating the transmembrane peptide. The purified building blocks were condensed in DMSO in the presence of silver chloride, 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine (HOOBt), N,N-diisopropylethylamine to give the product, Sub.c, after removal of Boc groups (yield 16%). The yield of the condensation reaction could be improved to 23% by raising the reaction temperature to 50 degrees C, and to 26% when a mixture of chloroform and methanol was used as a solvent.

Analysis of higher polyamide-6 oligomers on a silica-based reversed-phase column with a gradient of formic acid as compared with hexafluoroisopropanol

The analysis of polyamide-6 oligomers and polymer is usually performed with expensive fluorinated alcohols like 2,2,2-trifluoroethanol (TFE) or 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). Formic acid is well known as a mobile phase additive to adjust pH in reversed-phase high-performance liquid chromatography. However, formic acid is seldom used as a modifier to perform gradient elution chromatography on octadecyl-modified silica-based columns. Here we demonstrate the determination of cyclic and linear polyamide-6 oligomers using formic acid as a modifier on an octadecyl-modified silica-based column. This column was shown to be stable for more than 5000 column volumes, even when a mobile phase of 65-95% formic acid in water at a flow of 1 ml/min is applied. With formic acid under the conditions used (65-95% formic acid in water) the oligomers are retained on the column, while the polymer does not precipitate. In comparison, during adsorption and separation with a HFIP gradient, precipitation of the polymer occurs. The implications of the different separation mechanisms, i.e., adsorption vs. precipitation chromatography are discussed. Loadability is shown to be much better with the formic acid system. However, with formic acid as a modifier UV detection below 250 nm is not feasible. The less sensitive evaporative light scattering detector is used to detect the polyamide oligomers in the formic acid phase. In addition it is shown that capillary zone electrophoresis (CZE) with UV-absorbance detection using HFIP is an attractive combination as HFIP is UV-transparent and CZE allows low modifier consumption.

Purification and analysis of RTI40, a type I alveolar epithelial cell apical membrane protein

RTI40 is a 40-42 kDa protein that, within the lung, is specific to the apical plasma membrane of the rat alveolar type I cell. Type I cells cover greater than 95% of the internal surface area of the lung. In this report, we describe some of the physical properties of RTI40, and its purification to homogeneity. By liquid phase isoelectric focusing, the pI of the protein is 3.0+/-0.5. In two-dimensional immunoblots, there is a 1.0 pH unit charge train, suggesting post-translational modification of the protein. We have purified the protein to homogeneity by the following method. A membrane preparation from perfused rat lungs was extracted with detergent and applied to an ion-exchange column. Immunoreactive fractions from the column were pooled, dialyzed and further fractionated by reverse phase high performance liquid chromatography (HPLC). Essentially all the antigenicity was recovered in one protein peak that was homogeneous both by spectral analysis and silver-stained polyacrylamide gels. Because the purified protein was N terminus blocked, we cleaved the protein with CNBr and fractionated peptide fragments by reverse phase HPLC. Fractions were pooled and concentrated. Direct amino acid sequencing of the major peptide fragment yielded a 15 amino acid peptide homologous to a mouse osteoblast protein, OTS-8. Analysis of purified RTI40 shows that the protein contains glycan, some of which is sialic acid. Characterization of RTI40 should facilitate future studies of the functional properties of RTI40.

Electrospray-ionization mass spectrometry of intact intrinsic membrane proteins

Membrane proteins drive and mediate many essential cellular processes making them a vital section of the proteome. However, the amphipathic nature of these molecules ensures their detailed structural analysis remains challenging. A versatile procedure for effective electrospray-ionization mass spectrometry (ESI-MS) of intact intrinsic membrane proteins purified using reverse-phase chromatography in aqueous formic acid/isopropanol is presented. The spectra of four examples, bacteriorhodopsin and its apoprotein from Halobacterium and the D1 and D2 reaction-center subunits from spinach thylakoids, achieve mass measurements that are within 0.01% of calculated theoretical values. All of the spectra reveal lesser quantities of other molecular species that can usually be equated with covalently modified subpopulations of these proteins. Our analysis of bovine rhodopsin, the first ESI-MS study of a G-protein coupled receptor, yielded a complex spectrum indicative of extensive molecular heterogeneity. The range of masses measured for the native molecule agrees well with the range calculated based upon variable glycosylation and reveals further heterogeneity arising from other covalent modifications. The technique described represents the most precise way to catalogue membrane proteins and their post-translational modifications. Resolution of the components of protein complexes provides insights into native protein/protein interactions. The apparent retention of structure by bacteriorhodopsin during the analysis raises the potential of obtaining tertiary structure information using more developed ESI-MS experiments.

Mass spectrometry of whole proteins eluted from sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels

In this report we describe a novel approach to the mass spectrometric analysis of whole proteins from gels. The strategy consists of three components: conventional SDS-PAGE gels, reversible negative staining procedures, and passive elution of proteins from gels followed by mass spectrometric analysis. Protein bands are excised from SDS-PAGE gels, destained, and extracted. For gel loadings > or = 25 pmol of soluble protein, the proteins can be directly extracted into a solution consisting of formic acid/water/2-propanol. The recovered protein is suitable for matrix-assisted laser desorption/ionization (MALDI) or electrospray ionization mass spectrometric analysis. For gel loadings < 25 pmol protein, the mass spectrometric response, using the direct extraction procedure, drops off sharply, an outcome that is attributed to protein recovery losses. To offset the protein losses, the extraction procedure is slightly modified by performing the passive extraction of the gel with a saturated MALDI matrix solution. During the extraction period, the matrix is allowed to crystallize, forming a suspension in solution. Protein that elutes from the gel has a chance to cocrystallize with the matrix that can be retrieved for MALDI-MS analysis. This method of "capturing" eluted protein into matrix crystals is sensitive to 1 pmol of recombinant mouse leptin protein (16 kDa) loaded onto SDS-PAGE gels and can be used for proteins as large as 70 kDa. Our strategy has particular application to the characterization of endogenous forms of mature proteins from SDS-PAGE gels.

Comparative evaluation of the synthesis and purification of transmembrane peptide fragments. Rat bradykinin receptor fragment 64-97 as model

The 34-residue peptide CTVAEIYLGNLAGADLILASGLPFWAITIANNFD (TM-34), corresponding to the 64-97 sequence of the rat bradykinin, receptor, was selected as a model of hydrophobic transmembrane peptide segment for systematic study of synthesis and purification strategies. Application of conventional Boc/Bzl chemistry resulted in very low yield of the synthesis (around 4%) when DMF was used as the solvent for coupling reactions. As shorter resin-bound fragments of TM-34 showed improved swelling in 80% NMP/DMSO, the synthesis was repeated in this mixed solvent and the yield increased to 12%. A comparative synthesis using optimized Fmoc chemistry and Fmoc-(FmocHmb) derivatives of Ala and Leu to prevent aggregation did not provide any detectable TM-34. Taken together, these results illustrate the synthetic problems associated with hydrophobic sequences, almost regardless of the chemistry used. As expected, the hydrophobicity of TM-34 and of most of its minor fragments made them scarcely soluble in common solvents. Purification could be achieved by loading the crude materials dissolved in 90% AcOH onto a C4 HPLC column and eluting with a TFA/MeCN linear gradient. CD studies of the TM-34 and of the shorter fragment with the 74-97 sequence (TM-24) showed a higher percentage of alpha-helix structure for the latter. This suggests that the shorter sequence may better represent the correct transmembrane region of the second helix of the rat bradykinin receptor.

Purification of hydrophobic integral membrane proteins from Mycoplasma hyopneumoniae by reversed-phase high-performance liquid chromatography

A general and practical approach for isolating, fractionating and purifying large quantities of outer membrane hydrophobic proteins is described as applied to membrane proteins of Mycoplasma hyopneumoniae. Outer membrane proteins were extracted with Triton X-114 detergent and were precipitated from the detergent phase with 90% ethanol. Precipitated proteins were dissolved in 65% formic acid and separated by RP-HPLC using a formic acid-acetonitrile gradient. A M(r) 48 000 protein was obtained in high yield and at greater than 90% purity by optimisation of parameters for RP-HPLC. The combination of Triton X-114 extraction followed by high resolution RP-HPLC is a novel and rapid procedure for the isolation and purification of hydrophobic proteins. Proteins purified by this approach were suitable for subsequent characterisation by direct sequencing of the amino terminus as well as generation of peptides by digestion with cyanogen bromide.

Perfusion liquid chromatography of whey proteins

A perfusion reversed-phase (RP) HPLC method was developed for the rapid separation of the main bovine whey proteins: alpha-lactalbumin (alpha-LA), serum albumin (BSA) and the genetic variants of beta-lactoglobulin (A and B) (beta-LG A and beta-LG B). For the method development, the influence of factors favouring structural changes of proteins (temperature and organic acid concentration in the mobile phase), gradient and other chromatographic conditions and the mass of protein injected was examined. The optimized method allowed the separation of proteins in about 1.5 min (cycle time 3.5 min) with resolution around 1.0 for the beta-lactoglobulins. The method was applied to the determination of proteins in a whey from raw bovine milk. The precision of the determinations was < or = 3.75 mg per 100 ml (S.D.). With respect to the accuracy, errors < or = 7.0% in the determination of alpha-LA, beta-LG A and beta-LG B were obtained, compared with an RP-HPLC reference method. However, higher errors in the quantification of BSA were found owing to the lack of purity of the peak assigned. In addition, the proposed method has proved to be very useful in the detection of homologous whey proteins from different species (cow, sheep and goat) in milk mixtures.

High-performance liquid chromatographic purification of extremely hydrophobic peptides: transmembrane segments

Transmembrane peptides of integral membrane proteins often exhibit extremely high hydrophobicity. Therefore, the solubility of such peptides in solvents commonly used in HPLC is usually very low and the interaction with generally applied stationary phases such as silica gel or C18 reversed phases appears to be extremely strong, which makes the characterization and purification of these peptides difficult. The analytical characterization and preparative separation of the synthesized M1 transmembrane sequence of the inhibitory glycine receptor M(r) 48,000 subunit and some of its fragments is shown. M1 and its larger fragments could be dissolved in a dichloromethane-hexafluoro-2-propanol mixture containing a trace amount of pyridine for their separation on a C4 phase by employing linear two-component gradients of formic acid-2-propanol and formic acid-water with ratios up to 4:1 (v/v). Conditions to avoid formylation of the peptides are indicated.

Effect of glycation on the heterogeneity of human serum albumin analysed by reversed-phase high-performance liquid chromatography in a solvent containing formic acid

Non-enzymic glycation of human serum albumin (HSA) induces a change in its charge heterogeneity that may account for its particular renal clearance in patients with early diabetic nephropathy. A new high-performance liquid chromatographic analysis for the study of HSA heterogeneity is described based on a high content of formic acid in the mobile phase combined with a concave gradient of isopropanol. Under these conditions, native HSA was separated into three individual components (I, II and III). When glycated HSA was analysed, it was found that although the present method is not suitable for the separation of glycated from non-glycated HSA, it shows the effect of glycation in producing changes in HSA heterogeneity that are different from those reported on surface change. This finding suggests an additional factor (probably conformational changes) that is contributing to the heterogeneity of glycated HSA.

Alternative mobile phases for the reversed-phase high-performance liquid chromatography of peptides and proteins

The use of a high content of acetic acid as mobile phase additive for the reversed-phase high-performance liquid chromatography (RP-HPLC) of several proteins and extracts of biological tissues was evaluated for a divinylbenzene (DVB)-based stationary phase, and the separations obtained with acetic acid gradients in acetonitrile, isopropanol or water were compared with classical polypeptide RP-HPLC on silica C4 with trifluoroacetic acid (TFA)-acetonitrile. The separation patterns for recombinant derived interleukin-1 beta (IL-1 beta) on the C4 column eluted with TFA-acetonitrile and the DVB column eluted with acetic acid-acetonitrile were similar, but only the polymeric column was able to separate the components present in an iodinated IL-1 beta preparation. Neither eluent had any harmful effect on the biological activity of IL-1 beta isolated after RP-HPLC. Several standard proteins could be separated when the polymeric column was eluted with acetic acid gradients in acetonitrile, isopropanol or water and, although the separation efficiency with acetic acid in water was lower than that in combination with classical organic modifiers, insulin, glucagon and human growth hormone (hGH) were eluted as sharp, symmetrical peaks. The recoveries of insulin and hGH were comparable for all three mobile phases (80-90%). The separation patterns obtained from a crude acetic acid extract of a normal and a diabetic, human pancreas analysed using acetic acid gradients with or without organic modifiers were found to be similar and comparable to those obtained on a silica C4 column eluted with an acetonitrile gradient in TFA. The principal differences resulted from the use of different UV wavelengths (215 nm for TFA-acetonitrile, 280 nm for acetic acid). Acetic acid extracts of recombinant derived hGH-producing Escherichia coli were separated on the DVB column eluted with an acetic acid gradient in water. Although the starting material was a highly complex mixture, the hGH isolated after this single-step purification was surprisingly pure (as judged by sodium dodecyl sulphate-polyacrylamide gel electrophoresis). Consequently several (pure) polypeptides and complex biological samples were separated on a polymeric stationary phase eluted with acetic acid gradients in water without the use of organic modifiers.

A high-yield method for the isolation of hydrophobic proteins and peptides from polyacrylamide gels for protein sequencing

A methodological approach is described which allows the isolation of hydrophobic and hydrophilic proteins and peptides in high yield. The technique consists of (1) preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis, (2) protein elution from polyacrylamide gels with an organic solvent mixture composed of formic acid/acetonitrile/isopropanol/H2O (50/25/15/10, v/v/v/v), and (3) purification of eluted proteins by size exclusion chromatography on a Superose 12 column using this organic solvent mixture as eluant. The efficiency of this technique was tested with radioactively labeled polypeptides. These proteins were reaction center from Chloroflexus aurantiacus, bacteriorhodopsin, halorhodopsin from Halobacterium halobium, bovine serum albumin, ovalbumin, alpha-chymotrypsinogen A, and cytochrome c. The elution recoveries from polyacrylamide gels were 77-95%; the final yield after chromatographic purification was still 67-76% (with one exception). Subsequent amino acid sequencing was possible without further sample treatment. The sensitivity of the method described was found to be at least 20-30 micrograms protein.

Molecular basis for linkage of a continuous and discontinuous neutralization epitope on the structural polypeptide VP2 of poliovirus type 1

We obtained neutralizing monoclonal antibodies against a continuous neutralization epitope on VP2 of poliovirus type 1 strain Mahoney by using a combined in vivo-in vitro immunization procedure. The antibody-binding site was mapped to amino acid residues within the peptide segment (residues 164 through 170) of VP2 by competition with synthetic peptide and sequencing of resistant mutants. Cross-neutralization of these mutants with another neutralizing monoclonal antibody revealed a linkage of the continuous epitope and a discontinuous neutralization epitope involving both loops of the double-loop structure of VP2 at the twofold axis on the surface of the virion.

Isolation of pertussis toxin subunit proteins by reverse-phase high-performance liquid chromatography and reconstitution of the holotoxin molecule

Reverse-phase high-performance liquid chromatography on a column of trimethylsilylated silica gel (TSK-TMS 250) was utilized for the isolation of the subunit proteins of pertussis toxin (PT). Recovery up to 95% was obtained for each of the five distinct subunits with a high degree of homogeneity as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. None of the individual subunit proteins exhibited PT-related leukocytosis-promoting activity or the ability to bind haptoglobin; however, these activities were partially restored when an equimolar mixture of the isolated subunit in 6 M guanidine-HCl was diluted from this chaotropic agent. The complex macromolecule subsequently isolated from the mixture displayed subunit composition and biological activities indistinguishable from those of native PT, indicating that the toxin molecule had been reassembled.

Correlation of protein retention times in reversed-phase chromatography with polypeptide chain length and hydrophobicity

The use of amino acid retention or hydrophobicity coefficients for the prediction of peptide retention time behaviour on hydrophobic stationary phases is based on the premise that amino acid composition is the major factor affecting peptide retention in reversed-phase chromatography. Although this assumption holds up well enough for small peptides (up to ca. 15 residues), it is now recognized that polypeptide chain length must be taken into account when attempting to equate retention time behaviour of larger peptides and proteins with their overall hydrophobicity. In the present study, we have examined the reversed-phase retention behaviour of 19 proteins of known sequence on stationary phases of varying hydrophobicity and ligand density. From the observed protein retention behaviour on C4, C8 and C18 stationary phases under gradient elution conditions, we have been able to correlate the observed retention times of proteins ranging in molecular weight from 3500 to 32,000 dalton and in chain length from 30 to 300 residues with their overall hydrophobicity (based on retention parameters derived from small peptides) and the number of residues in the polypeptide chain. The retention behaviour of the proteins on the C4, C8 and C18 columns was also compared to that obtained on supports containing lower ligand densities (phenyl ligands). The maintenance of native or partially folded protein conformation on the phenyl columns, resulting in lower retention times than would be expected for fully denatured proteins, underlined the importance of efficient protein denaturation for satisfactory correlation of protein retention times with protein hydrophobicity. In addition, the effectiveness of increasing temperature and/or ligand density of the stationary phase in denaturing proteins was also demonstrated.

Reversed-phase liquid chromatography of proteins with strong acids

Small organic acids are generally used as pairing agents at less than 1% concentration in reversed-phase chromatography (RPC) of proteins. When the protein is very hydrophobic and insoluble, as in the case of membrane proteins, up to 60% aq. formic acid has been used. This paper reports a study of the influence of acid concentration on both chromatographic retention and protein structure in RPC. Chromatographic retention increases in proportion to the concentration of organic acid in the mobile phase up to some intermediate concentration. Use of still higher concentrations of acid results in a sharp drop in chromatographic retention with a change in selectivity. The data indicate that the structure of proteins in strong acids are different from that in weak acids. This work examines the reason for this decrease in chromatographic retention at formic and trifluoroacetic acid concentrations above 30% (v/v). Spectroscopic studies show that protein conformation continuously changes with the addition of acid.

Separation of lipid-free egg yolk proteins by high-pressure liquid chromatography using solvents containing formic acid

A method for obtaining total protein patterns from lipid-containing systems, in particular egg yolk, is described. After dispersion of the yolk in 8 M guanidine hydrochloride solution, lipid is removed by extraction with chloroform-methanol and petrol. The protein solution is applied to a high-pressure liquid chromatograph and eluted with a gradient of formic acid, isopropanol, and acetonitrile. In measurements on a known yolk protein, duck apovitellenin I, the method did not cause irreversible formylation of N-terminal or other residues. The method was used (1) to compare protein patterns of whole yolk from hen and quail eggs; (2) to isolate and partially sequence quail apovitellenin I; and (3) to compare protein patterns of "white yolk" and "yellow yolk."

Separation of proteins by reversed-phase high-performance liquid chromatography. II. Optimizing sample pretreatment and mobile phase conditions

The effects of separation variables such as temperature, pH and composition of the mobile phase (including additives such as chaotropes, ion-pairing agents and surfactants), sample size and sample pretreatment for reversed-phase high-performance liquid chromatography (RP-HPLC) of proteins is examined. Experimental optimization of these parameters using the preferred instrumental and column conditions described previously lead to well behaved chromatographic performance for most proteins. This allowed us to achieve the required level of performance for the first dimension (RP-HPLC) separation of most protein samples by the chromatophoresis process.

Purification and characterization of a 22-kDa microsomal protein from rat parotid gland which is phosphorylated following stimulation by agonists involving cAMP as second messenger

Stimulation of secretion in exocrine glands by agonists involving cAMP as second messenger leads to the phosphorylation of the ribosomal protein S6 (protein I) and two other particulate proteins with apparent molecular masses of 24 kDa (protein II) and 22 kDa (protein III) [Jahn, R., Unger, C. & Söling, H. D. (1980) Eur. J. Biochem. 112, 345-352]. This report describes the purification and characterization of protein III. Solubilization studies indicate that protein III is an intrinsic membrane protein. It could be extracted from the endoplasmic reticulum membrane only with Triton X-100, SDS or concentrated formic or acetic acid. The purification of this protein involved extraction of the microsomes with Triton X-100, removal of the detergent by acetone precipitation, extraction of water-soluble proteins, lipids and lipoproteins, and preparative SDS polyacrylamide gel electrophoresis. The protein has a basic pI (greater than 8.7). For determination of the amino acid composition of protein III and for sequencing of its amino-terminal portion, the protein was electroeluted out off the gel, the detergent removed and the protein finally purified by reversed-phase HPLC. Protein III could be phosphorylated in vitro by the catalytic subunit of the cAMP-dependent protein kinase to a degree of approximately 0.14 mol phosphate/mol protein. The only phosphopeptide obtained after in vitro phosphorylation and subsequent tryptic or chymotryptic digestion was identical with the phosphopeptide obtained after stimulation of intact rat parotid gland lobules with isoproterenol. The sequence of this peptide was Lys-Leu-Ser(P)-Glu-Ala-Asp-Asn-Arg. It was confirmed by an analysis of the synthetic peptide following in vitro phosphorylation with cAMP-dependent protein kinase. The first 41 N-terminal residues of protein III were sequenced. So far no sequence homology with other known peptides or proteins could be found.

Isolation of an integral membrane glycoprotein by chloroform-methanol extraction and C3-reversed-phase high-performance liquid chromatography

Methodology is presented for the isolation of integral membrane proteins and applied to the purification of the major myelin glycoprotein, P0. This isolation scheme depends on the detergent solubilization of an isoosmotically extracted membrane fraction from sciatic nerve endoneurium, followed by the removal of lipids and detergent by chloroform/methanol extraction. The resulting membrane proteins are readily dissolved in acetic acid/water (1/1) and directly analyzed by reversed-phase high-performance liquid chromatography. The hydrophobic nature of the intrinsic membrane protein mixture results in strong binding to a C8 stationary phase, leading to poor resolution and yields. These problems can be eliminated by employing a C3 alkylsilane column, thereby allowing separation of the protein components and the isolation of P0. The purified P0 has an amino-terminal sequence that matches that predicted from nucleotide sequencing, and the glycoprotein contains the expected amount of sialic acid. This latter finding indicates that the isolation procedure is not detrimental to the complex-type oligosaccharide structure of P0 and should make the methodology readily applicable to the purification of other integral membrane proteins and glycoproteins.

Column liquid chromatography of integral membrane proteins

Biological membranes have as a major function the compartmentation of biological processes in cells and organelles. They consist of a bilayer of phospholipid molecules in which proteins are embedded. These integral membrane proteins, which cross the bilayer once or several times, generally have a higher than average hydrophobicity and tend to aggregate. Detergents are needed to remove integral membrane proteins from the lipid bilayer and they have to be present during further chromatographic purification. Predominantly, four modes of HPLC have been used alone or in combination for the purification of integral membrane proteins. These are based on differences of proteins in size (size-exclusion chromatography, SEC), electrostatic interaction (ion-exchange chromatography, IEC), bioaffinity (bioaffinity chromatography, BAC) and hydrophobic interaction (reversed-phase chromatography, RPC, and hydrophobic-interaction chromatography, HIC). SEC, IEC, BAC and HIC are used under relatively mild conditions, and buffer systems generally contain a non-ionic detergent. RPC generally has a denaturing effect on the protein and should preferably be used for the purification of integral membrane proteins smaller than 50 kD.

Chromatography of complex protein mixtures

This review has shown that a variety of chromatographic techniques are available for fractionating proteins. Fortunately, high-quality columns of every type described in this review are commercially available. Most water-soluble proteins may be eluted from size-exclusion, hydrophobic-interaction, ion-exchange, metal chelate, and bioaffinity columns with ease. When this is the case, high recovery and retention of biological activity are the norm. The exception is reversed-phase chromatography where the organic solvents and acids used in polypeptide elution denature many proteins. When problems do occur, they are generally the result of unique structural features of the protein. Very hydrophobic proteins have presented the biggest problem in that they are difficult to solubilize, particularly with retention of biological activity. It has been found that zwitterionic and non-ionic detergents are the most suitable solubilizing agents, but urea has also been used in cases where hydrophobic interacts are not as strong. Unfortunately, there is still an element of trial-and-error in selecting the most suitable solubilizing agent. Heterogeneous glycosylation of proteins also presents a problem. Both neutral and charged monosaccharides can be incorporated into proteins through multiple steps at several sites. Thus, there is the potential in a sample for a large number of glycoprotein species which have the same polypeptide backbone and differing amounts of oligosaccharide. A problem arises when size-exclusion, ion-exchange, hydrophobic-interaction, reversed-phase and bioaffinity systems begin to discriminate between these very similar glycoprotein species. Chromatographic peaks can become very broad, due to incomplete fractionation, and the polypeptide chain of interest can be associated with multiple peaks. The separation of glycoproteins requires much more study before logical procedures can be suggested for column selection and operation. Aggregated species are another class of proteins which present occasional problems. Multimeric proteins are adsorbed to sorbents by a series of forces, among which are hydrogen bonding, hydrophobic interactions, and electrostatic forces. These forces are also responsible for the maintenance of quaternary structure in proteins. When the same forces dominate both retention of protein structure and adsorption at the sorbent surface, the quaternary structure of the protein can be disrupted during elution. Very basic proteins also present a problem in some cases. Columns with residual negative charges, such as a silica-based reversed-phase column, adsorb anionic species so strongly that they are difficult to elute.(ABSTRACT TRUNCATED AT 400 WORDS)

High-performance liquid chromatography of membrane proteins

Various modes of high-performance liquid chromatography, gel filtration, ion-exchange chromatography, hydrophobic interaction chromatography, reversed-phase chromatography and metal chelate affinity chromatography, were investigated for the separation of membrane proteins. All were found applicable to membrane proteins, although the usefulness of each mode differed. For satisfactory results it was important to select appropriate elution conditions. The type and concentration of detergent was of special importance. The effects of other conditions, flow-rate, gradient steepness, type of buffer and salt, eluent pH, etc., were similar to those observed for soluble proteins.

Binding site of neutralizing monoclonal antibodies obtained after in vivo priming with purified VP1 of poliovirus type 1 is located between amino acid residues 93 and 104 of VP1

Three hybridomas obtained after in vitro stimulation of spleen cells of mice primed in vivo with purified VP1 of poliovirus type 1 (Mahoney) with the homologous virus produced antibodies which reacted with VP1 and immunoprecipitated and neutralized only the homologous virus. Evidence for the location of their binding sites was obtained by inhibition of virus neutralization and virus binding by a synthetic peptide comprising the amino acid sequence 93-104 of VP1 of poliovirus type 1 (Mahoney).

Reversed-phase high-performance liquid chromatography of red blood cell membranes

Three reversed-phase (Hi-Pore RP-318, Hi-Pore RP-304, and Bio-Gel TSK Phenyl-RP+) and one hydrophobic-interaction (Bio-Gel TSK Phenyl-5PW) columns were used in a Bio-Rad chromatography system to separate the membrane proteins of human erythrocytes. A linear gradient, starting with 0.05% trifluoroacetic acid and ending with 95% acetonitrile and 0.05% trifluoroacetic acid was used. The four columns demonstrated slightly different selectivities for the proteins in ghosts. These profiles were further altered when ghosts were solubilized with 0.1% sodium dodecyl sulfate. The columns with less hydrophobic packings and larger pore sizes appear to be best suited for reversed-phase analyses of erythrocyte membrane proteins. Detergent solubilization was unnecessary for good resolution of the protein components.

Synthesis of an adsorbed reversed-phase packing material for the separation of proteins and peptides

We have described the preparation and chromatographic evaluation of an adsorbed hydrophobic stationary phase suitable for reversed-phase chromatography of proteins and peptides. The synthetic procedure involves three steps: the adsorption of a polyamine to the silica surface; crosslinking of the adsorbed polyamine layer with a bis-phenyl difunctional epoxide; and the benzoylation of the remaining accessible amino groups. Performance of this chromatographic material compared favorably with SynChropak RP-8 silica (SynChrom, Linden, IN, U.S.A.) and was stable to 40% formic acid. Good separations were obtained between the components of sample mixtures containing proteins or the cyanogen bromide fragments of sperm whale myoglobin. However, in both cases, the adsorbed hydrophobic stationary phase was less retentive. Furthermore, this medium exhibited slightly different selectivity. Whereas the heme which was present in the cyanogen bromide digest of myoglobin desorbed as the second peak from the RP-8 column, it eluted last from the adsorbed stationary phase. Comparable performance, acid stability and alternate selectivity suggest that this material is an interesting alternative to organosilane reversed-phase coatings.

The identification of neotrypsinogens in samples of bovine trypsinogen

Isoelectric focusing of commercial samples of bovine trypsinogen detected a component with a lower isoelectric pH than that of trypsinogen. The isoelectric pH was 8.75 compared to 9.3 for trypsinogen, and the amount of the component varied from 16 to 41% of the total protein. The protein (24,000 Da) was converted to fragments of 13,800 and 10,500 Da on reduction with dithioerythritol, showing that the component was a modified form of trypsinogen containing a cleaved peptide bond. The cleavage site was established from the study of four polypeptide fragments which were isolated from the fully reduced and S-carboxymethylated trypsinogen. The molecular weights, amino acid compositions, and amino-terminal sequences of these fragments identified a cleavage of Lys 131-Ser 132, namely from a Ser-neotrypsinogen, or at Arg 105-Val 106, from a Val-neotrypsinogen. Val-neotrypsinogen was the more abundant of the two and was approximately 71% of the total neotrypsinogen in the trypsinogen sample. Both neotrypsinogens were converted to active trypsin molecules in high yields, showing that the zymogens closely resembled the conformation of intact trypsinogen. Presumably, the neotrypsinogens were produced during the isolation of the zymogen when pancreatic tissue was partly autolyzed and active trypsin was present.

Characterization of a solvent system for separation of water-insoluble poliovirus proteins by reversed-phase high-performance liquid chromatography

Formic acid in high concentration is an extremely potent solvent for proteins, particularly for hydrophobic ones. 60% Formic acid, necessary for solubilization of structural polypeptides of poliovirus and other proteins, modified at the cysteines, was used together with 2-propanol or acetonitrile as organic modifier for gradient elution in reversed-phase high-performance liquid chromatography. Several reversed-phase columns were tested. In each case, polypeptides were eluted quantitatively. It was demonstrated that this solvent system, with its high proportion of formic acid, did not affect the size, hydrophobicity and charge of the separated polypeptides. By injection into rabbits of poliovirus polypeptides, obtained in high purity by chromatography in the new solvent system, monospecific antibodies were induced, the specificity of which was determined by immunoprecipitation.