Separation and analysis of peptides and proteins

Thin Films of Lanthanide Stearates as Modifiers of the Q-Sense Device Sensor for Studying Insulin Adsorption

This article presents new possibilities of using thin films of lanthanide stearates as sorbent materials. Modification of the Q-sense device resonator with monolayers of lanthanide stearates by the Langmuir-Schaeffer method made it possible to study the process of insulin protein adsorption on the surface of new thin-film sorbents. The resulting films were also characterized by compression isotherms, chemical analysis, scanning electron microscopy, and mass spectrometry. The transition of stearic acid to salt was recorded by IR spectroscopy. Using the LDI MS method, the main component of thin films, lanthanide distearate, was established. The presence of Eu²⁺ in thin films was revealed. In the case of europium stearate, the maximum value of insulin adsorption was obtained, -1.67·10^-10 mole/cm². The findings suggest the possibility of using thin films of lanthanide stearates as a sorption material for the proteomics determination of the quantitative protein content in complex fluid systems by specific adsorption on modified surfaces and isolation of such proteins from complex mixtures.

The isolation of water-soluble natural products - challenges, strategies and perspectives

Covering period: up to 2019Water-soluble natural products constitute a relevant group of secondary metabolites notably known for presenting potent biological activities. Examples are aminoglycosides, β-lactam antibiotics, saponins of both terrestrial and marine origin, and marine toxins. Although extensively investigated in the past, particularly during the golden age of antibiotics, hydrophilic fractions have been less scrutinized during the last few decades. This review addresses the possible reasons on why water-soluble metabolites are now under investigated and describes approaches and strategies for the isolation of these natural compounds. It presents examples of several classes of hydrosoluble natural products and how they have been isolated. Novel stationary phases and chromatography techniques are also reviewed, providing a perspective towards a renaissance in the investigation of water-soluble natural products.

Preventive and therapeutic potential of peptides from cereals against cancer

Epidemiological studies have shown that regular consumption of food based on whole-grain cereals and their products is associated with reduced risks of various types of degenerative chronic diseases. Food proteins are considered an important source of nutraceutical peptides and amino acids that can exert biological functions to promote health and prevent disease, including cancer. There have been several reports on peptides with anti-tumour activity in recent years. Plant-derived peptides, such as rapeseed, amaranth and soybean lunasin have received main attention. In this review, we extend this vision to analyse the evidence of current advances in peptides in cereals such as wheat, maize, rice, barley, rye and pseudocereals compared with soybean. We also show evidence of several mechanisms through which bioactive peptide exerts anti-tumour activity. Finally, we report the current status of major strategies for the fractionation, isolation and characterisation of bioactive peptides in cereals.

BIOLOGICAL SIGNIFICANCE

In recent reports, it has been shown that peptides are an interesting alternative in the search for new treatments for cancer. One of the most studied sources of these peptides is food proteins; however, a review that includes more recent findings for cereals as a potential source of bioactive peptides in the treatment of cancer, the techniques for their isolation and characterisation and the assays used to prove their bioactivity is not available. This review can be used as a tool in the search for new sources of anti-cancer peptides. The authors have no conflicts of interest, financial or otherwise.

Scanning fluorescence correlation spectroscopy in model membrane systems

Fluorescence correlation spectroscopy (FCS) is an emerging technique employed in biophysical studies that exploits the temporal autocorrelation of fluorescence intensity fluctuations measured in a tiny volume (in the order of fL). The autocorrelation curve derived from the fluctuations can then be fitted with diffusion models to obtain parameters such as diffusion time and number of particles in the diffusion volume/area. Application of FCS to membranes allows studying membrane component dynamics, which includes mobility and interactions between the components. However, FCS encounters several difficulties like accurate positioning and stability of the setup when applied to membranes. Here, we describe the theoretical basis of point FCS as well as the scanning FCS (SFCS) approach, which is a practical way to address the challenges of FCS with membranes. We also list materials necessary for FCS experiments on two model membrane systems: (1) supported lipid bilayers and (2) giant unilamellar vesicles. Finally, we present simple protocols for the preparation of these model membrane systems, calibration of the microscope setup for FCS, and acquisition and analysis of point FCS and SFCS data so that diffusion coefficients and concentrations of fluorescent probes within lipid membranes can be calculated.

Anharmonic vibrational analysis of 3,4-diaminopyridine and 3-aminopyridine by density functional theory calculations

In this work, we will report a combined experimental and theoretical study on molecular structure and vibrational analysis of 3,4-diaminopyridine (3,4-DAP) and 3-aminopyridine (3-AP). The Fourier transform infrared and Fourier transform Raman spectra of 3,4-DAP were recorded in the solid phase. The molecular geometry, harmonic vibrational wavenumbers of 3-AP and 3,4-DAP in the ground-state have been calculated by using MP2 and density functional methods (B3LYP) using 6-311++G(d,p) as basis set. Predicted electronic absorption spectra 3,4-DAP from TD-DFT calculation have been analyzed comparing with the experimental UV-vis spectrum. The calculated HOMO and LUMO energies show that charge transfer occur in the molecule. A detailed interpretation of the infrared spectra of 3-AP and 3,4-DAP is reported. The theoretical spectrograms for FTIR and FT-Raman spectra of the title molecules have also been constructed. Comparison of the experimental spectra with anharmonic vibrational wavenumbers indicates that B3LYP results are more accurate.

Analysis of a chlorosulfolipid from Ochromonas danica by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (ToF) mass spectrometry (MS) is an established tool for analyzing high mass molecules, such as proteins, whereas it attracts far less interest in the field of lipid analysis. In the study reported here a new chlorosulfolipid (CSL), 3,8,12,15-tetrachloroeicosane-1,17,18-triyl tris(hydrogen sulfate), was identified from the alga Ochromonas danica and de novo characterized by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight (MALDI-QIT-ToF) MS in negative ion mode. This method provides an effective alternative for the analysis of compounds directly derived from organic cell extracts. For MALDI analyses several frequently used solid MALDI matrices as well as some ionic liquid matrices (ILMs) were tested to enhance the analyte response to UV-laser and its ionization. The molecular weight of the observed compound could be determined as Li-, Na- and K-adducts [M+Me-2H]-. The characteristic isotopic patterns of the measured ions and the well-allocated molecular fragments by MS1, MS2 and MS3 indicate the fourfold chlorination and threefold sulfation of the investigated compound. The MS fragmentation alongside of the chlorine-bearing C-atoms is accompanied by the generation of a double bond at the opposite fragment in MS1. This obtained fragmentation pattern provides an insight into the allocation of the chlorine-bearing C-atoms along the carbon chain.

Pressure-induced effects in the heterogeneous adsorption of insulin on chromatographic surfaces

The effect of increasing the average column pressure (ACP) on the heterogeneous adsorption of insulin variants on a C18-bonded silica was studied in isocratic reversed-phase HPLC. Adsorption isotherm data of lispro and porcine insulin obtained for values of the ACP ranging from 57 to 237 bar were fitted to the Langmuir-Freundlich and the Tóth equation. The resulting isotherm parameters, including the equilibrium adsorption constant and the heterogeneity index, were next used for the calculation of distribution functions characterizing the energy of interactions between the adsorbed insulin molecules and the stationary phase. It was observed that increasing the pressure by 180 bar causes a broadening of the distribution functions and a shift of the position of their maximum toward lower interaction energies. These findings suggest that, under high pressures, the insulin molecules interact with the stationary phase in a more diversified way than under low pressures. Additionally, the most probable value of the energy of the insulin-surface interactions becomes lower when the ACP increases. The pressure-induced changes in the interaction of insulin variants with the hydrophobic surface are attributed to a possible conformational flexibility of the molecular structure of this protein.

Role of mass spectrometry in the purification of peptides and proteins

Experiments were carried out to evaluate the fractionation of proteins and peptides according to mass. Model mixtures were separated by either reversed-phase or ion-exchange chromatography with mass spectrometry-compatible mobile phase additives. Fraction collection was triggered by the mass/charge ratio of each one of the components of the mixture. Chromatography was additionally monitored with a UV-Vis detector in order to compare the new technique with generally accepted in separations. The results indicated that adequate purification is achieved by this new technique. Fraction collection triggered by changes in the mass/charge ratio reduces sample handling and analysis time. This study demonstrates the utility of mass-directed fractionation of peptides and proteins when mass spectrometry-compatible mobile phase additives are used.

High-performance liquid chromatography--mass spectrometry and electron-capture dissociation tandem mass spectrometry of osteocalcin. Determination of gamma-carboxyglutamic acid residues

Two mass spectrometry methods, high-performance liquid chromatography combined on-line with electrospray ionization mass spectrometry (HPLC-ESI-MS) and electron-capture (EC) dissociation tandem mass spectrometry (MS-MS), were applied for structural analysis of bovine and human osteocalcins. Osteocalcin contains gamma-carboxyglutamic acid (Gla) residues, which bind metal ions, among its amino acids. Ethylenediaminetetraacetic acid (EDTA) was added to all samples in order to chelate bound metal ions. After elimination of interfering metal ions MS spectra became uncomplicated to interpret. EDTA is incompatible with ESI and it was removed from samples using either on-line HPLC or micropurification method. The number of Gla residues varies in osteocalcin. These subforms, which contain different amounts of Gla residues, were separated using the HPLC-ESI-MS method. In order to determine locations of Gla residues in human osteocalcin, which contained two Gla residues, dissociation MS-MS method was successfully applied.

Liquid chromatography-mass spectrometry and capillary electrophoresis combined approach for separation and characterization of multicomponent peptide mixtures. Application to crude products of leuprolide synthesis

A sequential combination of reversed-phase liquid chromatography-mass spectrometry (LC-MS) and capillary electrophoresis (CE) has been explored in order to perform separation and characterization of a multicomponent peptide mixture from the synthesis of leuprolide. The mixture was first analyzed and fractionated by LC-MS, and the collected fractions were subsequently separated by CE. Unambiguous identification of the electrophoretic peaks was achieved by injecting the collected fractions separately and spiking the leuprolide crude mixture. Furthermore, structural information about the components of the mixture provided by several semi-empirical migration models has been used to check the accuracy of the structures previously proposed by LC-MS. Combination of the two orthogonal techniques results in an enhancement of their individual selectivity characteristics.

Experimental studies of pressure/temperature dependence of protein adsorption equilibrium in reversed-phase high-performance liquid chromatography

The effect of the average pressure and temperature of the column on the adsorption equilibrium of insulin variants on a C8 bonded silica was studied in isocratic reversed-phase HPLC. Analytical injections of samples of four different insulins (bovine, porcine. Lys-Pro and human recombinant) were carried out at constant flow-rate but under increased average pressure. The temperature dependence of the retention parameters over the range 25-50 degrees C was studied under two different average column pressures (47 and 147 bar). Substantial increases of the retention time (up to 300%) were observed when the pressure and/or the temperature were increased. Similar adsorption-induced changes in the partial molar volume at constant temperature (deltaVm approximately 102 ml/mol) were found for all the variants studied. Furthermore, deltaVm was revealed to be practically independent of the temperature, which suggests that the temperature has no or very little influence on the mechanism of the pressure induced perturbations in the molecular structure of the solute. This conclusion was also derived from the observed temperature dependence of the logarithm of the retention factor (k) measured under different pressures. The relation between the temperature and In k was nonlinear with a parabolic shape. Moreover, the shapes of the plots corresponding to the low and high pressures were found to be exactly the same, except that the curves were vertically shifted, due to the difference between the two average column pressures. These results indicate that pressure and temperature affect the retention behavior of insulins in a different and separate way.

Electrophoretic behavior of peptides in capillary electrophoresis influence of ionic strength and pH in aqueous-organic media

Through correct pH, pKa and activity coefficients values, a model describing the effect of pH on electrophoretic mobility of substances has been applied to a series of peptides in water and in acetonitrile-water mixtures. The derived equations permit prediction of the optimum pH for the electrophoretic separation from only a few experimental values and they also permit determination of pKa values of analytes in the aqueous-organic media employed. Furthermore, the electrophoretic resolution between pairs of substances can be predicted, in order to evaluate electrophoretic separations of the studied peptides.

Geometric scaling effects in electrical field flow fractionation. 1. Theoretical analysis

This work outlines the fundamental scaling laws associated with electrical field flow fractionation channels. Although general FFF theory indicates few advantages from miniaturization, EFFF theory indicates clear advantages to miniaturization of the EFFF channel. Retention, plate heights, resolution, equilibration times, and time constants are examined. The outlined theory predicts scaling advantages in each of these areas after miniaturization. Potential applications, such as the use of these systems for sample preparation in microscale total analysis systems, and improvements associated with these theoretical predictions are also discussed.

Capillary electrophoresis for the analysis of food proteins of animal origin

In recent years, capillary electrophoresis (CE) has become an analytical technique with many applications in the study of food proteins and peptides. This review describes the existing CE methods of analysis of milk, egg, meat and fish proteins and peptides. The major developments in the application of CE to solve different problems in food technology, such as the assessment of technological processes, quality, and authenticity control of animal foods, are considered. A section dealing with future directions on the analysis of food proteins by CE is also included.

Separation and characterization of multicomponent peptide mixtures by liquid chromatography-electrospray ionization mass spectrometry. Application to crude products of the synthesis of leuprolide

Leuprolide is a synthetic structural analogue of luteinizing hormone-releasing hormone used for the treatment of a large number of diseases related with the regulation of sexual hormones. Solid-phase peptide synthesis is used to obtain leuprolide peptidic hormone, but this synthetic procedure results in complex mixtures that need separation and characterization. Here, liquid chromatography coupled with mass spectrometry using electrospray ionization, (LC-ES-MS), was used for the separation and characterization of multicomponent peptide mixtures of crudes of synthesis of leuprolide. To optimize the LC separation process, the method of linear solvation energy relationships was applied and the powerful coupling LC-ES-MS permitted rapid and reliable characterization of the reaction product.

Separation of potentially therapeutic peptide hormones by liquid chromatography. Optimisation of the composition and pH of the mobile phase

The aim of this work is to optimise the proportion of the organic modifier and the pH of the mobile phase, in order to separate a series of peptide hormones with therapeutic interest in the molecular mass range from 500 to 6000. The composition of the mobile phase was optimised by establishing relationships between retention parameters and either the scale of solvent polarity, or the Kamlet-Taft multiparameter solvent scale of the eluent, using linear solvation energy relationships. Likewise, linear correlations between the chromatographic retention and Reichardt's E(T)N parameter were obtained. These relationships allowed an important reduction of the experimental retention data needed for developing a given separation. In addition, a model describing the effect of the correctly measured pH of the mobile phase on retention in LC was established and tested for the series of selected peptides using an octadecylsilica column. The proposed equations permit the prediction of the optimum pH and also permit the determination of the acidity constants of the peptides in the hydro-organic mixtures using a minimum number of measurements.

Monitoring impurities in biopharmaceuticals produced by recombinant technology

The unique nature of recombinant technology and the biotherapeutic production process means that regulatory agencies around the world not only require extensive characterization of the product, but they have also provided 'guidelines' to control and monitor product- and process-derived impurities and contaminants. Not only might these impurities and contaminants have a profound effect on product quality and efficacy, but they might also introduce unwanted and unknown side effects, even in trace amounts. The authors present a comprehensive understanding of the nature of possible product- and process-related impurities, and also describe current and future methodologies to control and monitor these impurities.

Separation and identification of peptide mixtures in a synthesis crude of carbetocin by liquid chromatography/electrospray ionization mass spectrometry

In order to separate and characterize the target peptide and the side-product peptide compounds of a synthesis crude of the peptide hormone carbetocin, liquid chromatography coupled to high-flow electrospray ionization mass spectrometry (LC/eS-MS) has been used. Carbetocin is an important drug with recognized therapeutical application for stimulation of uterine contractions to facilitate parturition. Stepwise solid phase peptide synthesis (SPPS) commonly results in unwanted side products associated with incomplete peptide chains. Consequently, this procedure requires extensive purification and characterization of the final synthesis crude. The linear solvation energy relationship (LSER) method has been applied to optimize the proportion of organic modifier of the mobile phase used in the established LC method. On the other hand, ES-MS has allowed rapid and reliable identification of the target peptide and the other impurities present in the carbetocin synthesis products.

Capillary electrophoresis with laser-induced native fluorescence detection for profiling body fluids

Laser-induced native fluorescence detection with a KrF excimer laser (lambda=248 nm) was used to investigate the capillary electrophoretic (CE) profiles of human urine, saliva and serum without the need for sample derivatization. All separations were carried out in sodium phosphate and/or sodium tetraborate buffers at alkaline pH in a 50-microm I.D. capillary. Sodium dodecyl sulfate was added to the buffer for micellar electrokinetic chromatography (MEKC) analysis of human urine. Although inherently a pulsed source, the KrF excimer laser was operated at a high pulse repetition rate of 553, 1001 or 2009 Hz to simulate a continuous wave excitation source. Detection limits were found to vary with pulse rate, as expected, in proportion to average excitation power. The following detection limits (3sigma) were determined in free solution CE: tryptophan, 4 nM; conalbumin, 10 nM; alpha-lactalbumin, 30 nM. Detection limits for indole-based compounds and catecholamine urinary metabolites under MEKC separation conditions were in the range 7-170 nM.

Thin-layer ion-exchange chromatography of proteins

Thin-layer chromatography (TLC) is one of the simplest and most convenient techniques to separate small molecules. Of a variety of TLC separation modes, only size-exclusion was successfully used to separate proteins. In this paper, adsorption-TLC was used to separate proteins. The net charges were calculated for four model proteins, albumin, transferrin, lactoferrin and lysozyme, under different pH values. The suitable pH values for separation were determined according to the results from such calculations. Then, the adsorption isotherms of the four proteins were measured to deduce the ionic strength for appropriate elution conditions. Optimal conditions, 0.01 M bicine and pH 8.50, and a three-step elution process (1st step 0.01 M NaCl, 2nd 0.025 M NaCl, and 3rd 0.10 M NaCl), were obtained. Finally, the four model proteins were successfully separated under these elution condition.

Liquid chromatographic-high-resolution mass spectrometric and tandem mass spectrometric identification of synthetic peptides using electrospray ionization

Liquid chromatography-high-resolution electrospray mass spectrometry (LC-ESI-MS) was investigated for the identification of known and unknown synthetic peptides in a research effort designed to evaluate the applicability of this and complementary MS techniques for peptide characterization and identification. The monoisotopic molecular masses of five related peptides with molecular masses between 2000 and 2500 u were acquired with a resolution of 3000 (10% valley). Under narrow and wide mass range magnetic sector scanning conditions monoisotopic molecular mass errors were typically in the 10-20 and 30-40 ppm range, respectively. Tryptic maps were generated for each peptide following LC-ESI-MS analysis and collisionally activated dissociation (CAD) in the ESI interface resulted in the production of characteristic product ions that enabled amino acid sequencing of the tryptic fragments. Unknown identification was demonstrated during analysis of an incomplete synthetic peptide reaction mixture. The synthesis of an 18 amino acid peptide, LTTAVKKVLTTGLPALIS, was not successful. In its place were six unknown peptides that were identified on the basis of monoisotopic molecular mass and amino acid sequence data. The monoisotopic molecular masses of these unknowns were determined to within 10-20 ppm with a resolution of 3500 (10% valley). Amino acid sequences for the six peptides were generated during ESI-MS-MS analysis. Finally two synthetic peptides differing only by the incorporation of a 13C at leucine were analysed with a resolution of 6000 (10% valley) to confirm that the isotopic distributions were consistent with theoretical expectations.