Optimal conditions for the reversed-phase chromatography of proteins

Proteomics applied to transfusion plasma: the beginning of the story

'Safe blood' is and has always been the major concern in transfusion medicine. Plasma can undergo virus inactivation treatments based on physicochemical, photochemical or thermal methodologies for pathogen inactivation. The validation of these treatments is essentially based on clottability assays and clotting factors' titration; however, their impact on plasma proteins at the molecular level has not yet been evaluated. Proteomics appears as particularly adapted to identify, to localize and, consequently, to correlate these modifications to the biological activity change. At the crossroads of biology and analytical sciences, proteomics is the large-scale study of proteins in tissues, physiological fluids or cells at a given moment and in a precise environment. The proteomic strategy is based on a set of methodologies involving separative techniques like mono- and bidimensional gel electrophoresis and chromatography, analytical techniques, especially mass spectrometry, and bioinformatics. Even if plasma has been extensively studied since the very beginning of proteomics, its application to transfusion medicine has just begun. In the first part of this review, we present the principles of proteomics analysis. Then, we propose a state of the art of proteomics applied to plasma analysis. Finally, the use of proteomics for the evaluation of the impact of storage conditions and pathogen inactivation treatments applied to transfusion plasma and for the evaluation of therapeutic protein fractionated is discussed.

A universal, high recovery assay for protein quantitation through temperature programmed liquid chromatography (TPLC)

As an alternative to direct UV absorbance measurements, estimation of total protein concentration is typically conducted through colorimetric reagent assays. However, for protein-limited applications, the proportion of the sample sacrificed to the assay becomes increasingly significant. This work demonstrates a method for quantitation of protein samples with high recovery. Temperature programmed liquid chromatography (TPLC) with absorbance detection at 214nm permits accurate estimation of total protein concentration from samples containing as little as 0.75μg. The method incorporates a temperature gradient from 25 to 80°C to facilitate elution of total protein into a single fraction. Analyte recovery, as measured from 1 and 10μg protein extracts of Escherichia coli, is shown to exceed 93%. Extinction coefficients at 214nm were calculated across the human proteome, providing a relative standard deviation of 21% (versus 42% at 280nm), suggesting absorbance values at 214nm provide a more consistent measure of protein concentration. These results translate to a universal protein detection strategy exhibiting a coefficient of variation below 10%. Together with the sensitivity and tolerance to contaminants, TPLC with UV detection is a favorable alternative to colorimetric assay for total protein quantitation, particularly in sample-limited applications.

Mass spectrometric detection of proteins in non-aqueous media — The case of prion proteins in biodiesel

Limitations in efficient extraction, minimization of media interferences, and suitable sample preparation methods pose significant challenges to the successful detection of protein traces in non-aqueous media. Here we present a filtration method, employing filter disks with embedded C8-modified silica particles, that allows the capture of proteins from non-aqueous sample volumes. The extraction process is followed by elution of the protein from the filter disk and by either direct mass spectrometric detection or tryptic digestion followed by peptide mapping and MS/MS fragmentation of protein-specific peptides. The method is applied to spiked biodiesel samples for the detection of prion proteins. The tryptic peptide with sequence YPGQGSPGGNR is specific for prion proteins and can be used for unambiguous identification. The developed extraction method has the potential application to be used for large-scale testing of protein impurities in non-aqueous media, for instance as a safety and quality control tool in the animal tallow-based biodiesel production process.Key words: protein detection, MALDI, non-aqueous media, filtration

Factors affecting the separation and loading capacity of proteins in preparative gradient elution high-performance liquid chromatography

The optimum conditions for the purification of proteins by gradient elution in reversed-phase liquid chromatography were studied, with emphasis on the column length. Because of the strong dependence of the retention of proteins on the mobile phase composition, very short columns can be used successfully to perform analytical separations. A similar conclusion is extended to preparative separations. Columns with different lengths and diameters were used. The dependence of the loading capacity for touching band separation on the column length, diameter and volume was studied, in addition to the regeneration time between successive runs, the starting mobile phase composition and the necessary column efficiency.

Hydrophilic-interaction chromatography for the separation of peptides, nucleic acids and other polar compounds

When a hydrophilic chromatography column is eluted with a hydrophobic (mostly organic) mobile phase, retention increases with hydrophilicity of solutes. The term hydrophilic-interaction chromatography is proposed for this variant of normal-phase chromatography. This mode of chromatography is of general utility. Mixtures of proteins, peptides, amino acids, oligonucleotides, and carbohydrates are all resolved, with selectivity complementary to those of other modes. Typically, the order of elution is the opposite of that obtained with reversed-phase chromatography. A hydrophilic, neutral packing was developed for use in high-performance hydrophilic-interaction chromatography. Hydrophilic-interaction chromatography is particularly promising for such troublesome solutes as histones, membrane proteins, and phosphorylated amino acids and peptides. Hydrophilic-interaction chromatography fractionations resemble those obtained through partitioning mechanisms. The chromatography of DNA, in particular, resembles the partitioning observed with aqueous two-phase systems based on polyethylene glycol and dextran solutions.

Unexpected elution behaviour of peptides with various reversed-phase columns

Gastrin and cholecystokinin peptides were separated by reversed-phase chromatography on conventional bristle-type and polymer-coated stationary phases. The retention of the sulphated and non-sulphated isomeric forms of both peptides is governed by the structure of the peptide, the net charge and additional polar interactions with the stationary phases. Polymer-coated phases are optimum for separations according to chain length, whereas polar interactions are required for the separation of sulphated and non-sulphated peptides of identical chain length.

Improvement in the resolution of o-phthalaldehyde derivatized amino acids by applying gradient steepness optimization to five reversed-phase columns of different lengths and particle sizes

Twenty-two o-phthalaldehyde (OPA) derivatized amino acids were separated on five different reversed-phase, octadecyl columns. Each column was packed with the same type of spherical silica on which matched bonding chemistry had been performed. Columns of 250, 150 or 50 mm x 4.5 mm I.D. were packed with 5 microns particles, and columns of 100 or 50 mm x 4.5 mm I.D. were packed with 3 microns particles. Snyder's linear solvent strength gradient optimization method was used to determine the optimum gradient steepness by maximizing the resolution of four pairs of adjacent OPA-derivatized amino acids. An asymptotic dependence of improvement in resolution with increase in gradient time was obtained for each pair of compounds on each column. For short (50 mm) columns, resolution of very closely eluting compounds required the use of gradient steepness parameters as low as 0.05 and 0.02, due to the low efficiencies intrinsic to these short column lengths.

Evaluation of advanced silica packings for the separation of biopolymers by high-performance liquid chromatography. III. Retention and selectivity of proteins and peptides in gradient elution on non-porous monodisperse 1.5-microns reversed-phase silicas

Following previous studies of the use of non-porous monodisperse 1.5-microns n-octyl- and n-octadecyl-bonded silicas in gradient elution of proteins, this work was aimed at elucidating further the properties of this novel column material for peptide and protein separations in comparison with wide-pore silicas. First, it is demonstrated that with short columns (e.g., 35 X 8 mm I.D.) packed with these non-porous reversed-phase materials, mixtures of small peptides and mixtures of proteins can be very efficiently resolved. When the chain length of the bonded ligand was varied, the retention of a test set of proteins in gradient elution followed the ligand sequence C18 greater than C8 approximately C4 approximately phenyl greater than C2 under constant elution conditions, and the selectivity remained unchanged. Comparison of the S values of these proteins, as determined from evaluation of the log k' vs. phi dependences with non-porous silicas and with a LiChrospher Si 1000 C8 with identical accessible ligand surface areas per unit column volume, indicated lower values for the non-porous materials (k' = capacity factor; phi = molar fraction of organic solvent; S = slope of the plot of log k' vs. phi). The origin of this behaviour is discussed.

Effect of mass loadability, protein concentration and n-alkyl chain length on the reversed-phase high-performance liquid chromatographic behaviour of bovine serum albumin and bovine follicular fluid inhibin

The chromatographic behaviour of bovine serum albumin and partially purified preparations of the 58 kilodalton form of bovine follicular fluid inhibin has been investigated using two different n-alkylsilica stationary phases. In particular, the effects of mass loadability, protein concentration and loading conditions on the relative retention, peak width and recovery of these proteins have been studied over a dynamic range up to 100 mg protein per g packing material per injection. The influence of variable amounts of more abundant contaminating proteins such as bovine serum albumin in crude inhibin preparations on the chromatographic purification of trace quantities of the 58 kilodalton inhibin protein has also been examined. Based on these observations, recommendations are offered for the selection of protein loading conditions with n-alkylsilica stationary phases, particularly for the trace recovery and purification of hydrophobic proteins similar to inhibin where self-aggregation, adsorption to glass or plastic surfaces, and aberrant chromatographic behaviour on size exclusion or adsorptive chromatographic supports may occur.

High-speed and high-performance size-exclusion chromatography of proteins on a new hydrophilic polystyrene-based resin

High-performance size-exclusion chromatography of some standard proteins, peptides and amino acids on a new hydrophilic packing material obtained by chemical transformation of a cross-linked polystyrene-divinylbenzene copolymer was studied. Columns filled with 4 and 7 micron particles were compared. The influence of the concentration of acetonitrile, isopropanol and trifluoroacetic acid in the mobile phase on the chromatographic performance was investigated. A good linear calibration graph covering the molecular weight range from 200 to 700,000, was obtained under the optimal conditions. The packing material can be used for separations, for molecular weight determinations and for the pre-fractionation of proteins. The high rigidity of the packing material allows relatively high pressures to be used and therefore fast separations to be achieved. The packing material was applied to the chromatography of proteins from beer, bones and milk.