Development of a rapid, efficient, and reusable magnetic bead-based immunocapture system for recombinant human procollagen type II isolation from yeast fermentation broth.

Recombinant collagen production, especially using yeasts as expression systems, could represent a promising alternative over traditional extractive methods from animal sources, offering controllable, scalable, and high-quality products. Monitoring the efficiency and efficacy of procollagen/collagen expression, especially in the initial fermentation phases, can be difficult and time consuming, as biological matrices necessitate purification and commonly used analytical methods are only partially informative. We propose a straightforward, efficient, and reusable immunocapture system able to specifically isolate human procollagen type II from fermentation broths and to release it in few experimental steps. A recovered sample allows for a detailed characterization providing information on structural identity and integrity, which can strongly support the monitoring of fermentation processes. The immunocapture system relies on the use of protein A-coated magnetic beads which have been functionalized and cross-linked with a human anti-procollagen II antibody (average immobilization yield of 97.7%) to create a stable and reusable support for the specific procollagen fishing. We set up the binding and release conditions ensuring specific and reproducible binding with a synthetic procollagen antigen. The absence of non-specific interaction with the support and binding specificity was demonstrated, and the latter was also confirmed by a peptide mapping epitope study in reversed-phase liquid chromatography high-resolution mass spectrometry (RP-LC-HRMS). The bio-activated support proved to be reusable and stable over 21 days from the initial use. Finally, the system was successfully tested on a raw yeast fermentation sample to provide a proof of concept of the applicability within recombinant collagen production.

Bio-Guided Fractionation of Stem Bark Extracts from Phyllanthus muellarianus: Identification of Phytocomponents with Anti-Cholinesterase Activity.

A combination of flash chromatography, solid phase extraction, high-performance liquid chromatography, and in vitro bioassays was used to isolate phytocomponents endowed with anticholinesterase activity in extract from Phyllanthus muellarianus. Phytocomponents responsible for the anti-cholinesterase activity of subfractions PMF1 and PMF4 were identified and re-assayed to confirm their activity. Magnoflorine was identified as an active phytocomponent from PMF1 while nitidine was isolated from PMF4. Magnoflorine was shown to be a selective inhibitor of human butyrylcholinesterase-hBChE (IC50 = 131 ± 9 µM and IC50 = 1120 ± 83 µM, for hBuChE and human acetylcholinesterase-hAChE, respectively), while nitidine showed comparable inhibitory potencies against both enzymes (IC50 = 6.68 ± 0.13 µM and IC50 = 5.31 ± 0.50 µM, for hBChE and hAChE, respectively). When compared with the commercial anti-Alzheimer drug galanthamine, nitidine was as potent as galanthamine against hAChE and one order of magnitude more potent against hBuChE. Furthermore, nitidine also showed significant, although weak, antiaggregating activity towards amyloid-ß self-aggregation.

Affinity-based separation methods for the study of biological interactions: The case of peroxisome proliferator-activated receptors in drug discovery.

Affinity-based methods using immobilized proteins are important approaches for understanding the interactions between small molecules and biological targets. This review is intended to provide an overview of different affinity based separation methods that have been applied to the study of peroxisome proliferator activated receptors (PPARs). The screening of compound to increase screening rates for synthetic and natural ligands of PPAR are reported. Pros and cons of the approaches in ligand discovery initiatives are discussed.

Characterization of intact neo-glycoproteins by hydrophilic interaction liquid chromatography.

In this study, an HPLC HILIC-UV method was developed for the analysis of intact neo-glycoproteins. During method development the experimental conditions evaluated involved different HILIC columns (TSKgel Amide-80 and ZIC-pHILIC), and water-acetonitrile mixtures containing various types of acids and salts. The final selected method was based on a TSKgel Amide-80 column and a mobile phase composed of acetonitrile and water both containing 10 mM HClO4. The influence of temperature and sample preparation on the chromatographic performances of the HILIC method was also investigated. The method was applied to the separation of neo-glycoproteins prepared starting from the model protein RNase A by chemical conjugation of different glycans. Using the method here reported it was possible to monitor by UV detection the glycosylation reaction and assess the distribution of neo-glycoprotein isoforms without laborious sample workup prior to analysis.

Combination of a solid phase extraction and a two-dimensional LC-UV method for the analysis of vitamin D3 and its isomers in olive oil.

The current HPLC methods for the quantification of vitamin D3 (VitD3) and its two isomers previtamin D3 (PreVitD3) and trans-vitamin D3 (trans-VitD3) in olive oil preparations present some limitations mainly due to peak overlapping of the oily matrix components with the compounds of interest. The use of two-dimensional liquid chromatography (2D-LC) with different retention mechanism can reach higher resolving power thus allowing the analysis of complex samples. The present paper proposes a new alternative method including a solid phase extraction sample preparation step and a two-dimensional liquid chromatographic analysis using routine instrumentation, fitting the needs of quality assurance and quality control laboratories of pharmaceutical companies. The extraction protocol was demonstrated to provide a clean-up of the sample and a quantitative recovery of the species of interest. The 2D method proved its suitability in the isolation of vitamins from oil components in the first dimension and the separation and quantification of the analytes in the second dimension thanks to the orthogonal selectivities of phenyl and porous graphitic carbon (PGC) stationary phases. The method was validated following ICH guidelines and possesses an adequate sensitivity to quantify the impurity trans-VitD3 in pharmaceuticals considering the limits imposed by regulatory agencies. The applicability of the phenyl x PGC 2D-LC-UV method to quality control of medicinal products based on VitD3 in olive oil was confirmed by the successful quantification of vitamins in olive oil formulations.

Chromatographic separation by RPLC-ESI-MS of all hydroxyproline isomers for the characterization of collagens from different sources.

During collagen biosynthesis, proline is post-translationally converted to hydroxyproline by specific enzymes. This amino acid, unique to collagen, plays a crucial role in stabilizing the collagen triple helix structure and could serve as an important biomarker for collagen content and quality analysis. Hydroxyproline has four isomers, depending on whether proline is hydroxylated at position 4 or 3 and on whether the cis- or trans- conformation is formed. Moreover, as extensive hydrolysis of collagen is required for its amino acid analysis, epimerization may also occur, although to a lesser extent, giving a total of eight possible isomers. The aim of the present study was to develop a reversed-phase high-performance liquid chromatography-UV-mass spectrometry (RPLC-UV-MS) method for the separation and quantification of all eight hydroxyproline isomers. After the chiral derivatization of the hydroxyproline isomers with Nα-(2,4-dinitro-5-fluorophenyl)-L-valinamide (L-FDVA), to enable their UV detection, the derivatized diastereoisomers were separated by testing different C18 column technologies and morphologies and optimizing operative conditions such as the mobile phase composition (solvent, additives), elution mode, flow rate and temperature. Baseline resolution of all eight isomers was achieved on a HALO® ES-C18 reversed-phase column (150×1.5 mm, 2.7 µm, 160 Å) using isocratic elution and MS-compatible mobile phase. The optimized method was validated for the quantification of hydroxyproline isomers and then applied to different collagen hydrolysates to gain insight and a deeper understanding of hydroxyproline abundances in different species (human, chicken) and sources (native, recombinant).

Direct glycosylation analysis of intact monoclonal antibodies combining ESI MS of glycoforms and MALDI-in source decay MS of glycan fragments.

Monoclonal antibody (mAb) glycoengineering has the potential to improve the efficacy of biopharmaceuticals by fine-tuning specific biological properties. Glycosylation analysis is key to monitoring the glycoengineering process. Various mass spectrometry (MS)-based methods are available to characterize mAb glycosylation at different structural levels, but comprehensive analysis is typically time-consuming and costly. Here, we present an approach that combines conventional intact mass measurement of glycoforms by direct infusion ESI-MS with an advanced MALDI-in-source decay FT-ICR MS method for direct analysis of glycans in intact mAbs, without the need for enzymatic release and separation. Using a sodium-doped MALDI matrix, glycans were directly released as ISD fragment ions from the intact mAbs during the ionization process. Measurement of 0,2A fragment signals yielded reproducible glycan profiles that were consistent with conventional methods, yet was achieved with unprecedented speed, providing complementary information to that obtained through intact mass measurement. The methods were applied to standard and glycoengineered trastuzumab and rituximab, allowing rapid glycosylation profiling and structural analysis of glycans by tandem MS of selected ISD fragment ions. This fast approach can facilitate the early-phase development of glycoengineering processes by constraining further in-depth analyses. We envision a broader applicability in studies focused on glycosylation changes in mAbs.

Development of new chromatographic tools based on A2A adenosine receptor subtype for ligand characterization and screening by FAC-MS.

A liquid chromatographic stationary phase containing immobilized membranes from cells expressing A(2A) adenosine receptor (A(2A)AR) is firstly described. Cellular membranes from CHO cells stably transfected with human A(2A)AR vector (A(2A)(+)) and from the same cell line transfected with the corresponding empty vector (A(2A)(-)) were entrapped on immobilized artificial membrane (IAM) support and packed into 6.6 mm I.D. glass columns to create A(2A)(+)-IAM and A(2A)(-)-IAM stationary phases. Frontal chromatography experiments on both A(2A)(+)-IAM and A(2A)(-)-IAM columns demonstrated the presence of a low specific interaction with the receptor. However, immobilized A(2A) retained its ability to specifically bind known ligands as demonstrated by the agreement of the calculated K(d) values with two different chromatographic protocols in comparison to previously reported data. In order to maximize the specific interaction, the same cellular membranes were immobilized on the inner surface of a silica capillary (40 cm × 100 µm I.D.) by non-covalent interactions using the avidin-biotin coupling system to create two open tubular columns A(2A)(+)-OT and A(2A)(-)-OT. The open tubular system was characterized by ranking experiments for affinity studies in mixture useful for the selection of new potential candidates.

Column comparison and method development for the analysis of short-chain carboxylic acids by zwitterionic hydrophilic interaction liquid chromatography with UV detection.

Short-chain carboxylic acids are relevant in pharmaceutical, food quality control, and biomedical analysis. In this study, 11 acids commonly found in drugs and in food products were selected. Wine was chosen as matrix for testing the method. The test compounds were used for comparing the selectivity of four 150 × 2.1 mm zwitterionic hydrophilic interaction LC (HILIC) columns (ZIC-HILIC 5 µm, 200 Å, and 3.5 µm, 100 Å, ZIC-pHILIC 5 µm, ZIC-cHILIC 3 µm, 100 Å) while varying the conditions to optimize for low UV wavelength detection and achieve high sensitivity. Retention using potassium phosphate and ammonium carbonate as mobile-phase components at pH 6.0, 7.5, and 8.5-8.9 was studied considering recent hypotheses on HILIC mechanism-related with the Hofmeister series effect and ion hydration. An isocratic method with UV detection at 200 nm and mobile phase consisting of 75% acetonitrile and 10 mM potassium phosphate at pH 6.0 applied to a ZIC-cHILIC column was found provisionally optimal and partially validated for the 11 analytes. Satisfactory results (R(2) from 0.9940 to >0.9999), and recoveries from 93-106% for all analytes evidenced the method as suitable for wine analysis. To the best of our knowledge, no previous study has reported on the direct ZIC-HILIC separation and UV detection of the acids considered here in wine.

Synthesis, Characterization and Application of a MIP-polyHIPE for Selective Extraction of Angiotensin II Receptor Antagonists Residues in Natural Waters.

Polymers via high internal phase emulsion (polyHIPEs) were molecularly imprinted with Irbesartan, an antihypertensive drug belonging to the class of angiotensin II receptor antagonists (sartan drugs), chosen for the proof-of-concept extraction of hazardous emerging contaminants from water. Different analyte-functional monomer molar ratios (1:100, 1:30 and 1:15) were investigated, and the MIP polyHIPEs have been characterized, parallel to the not imprinted polymer (NIP), by batch sorption experiments. The material with the highest template-functional monomer ratio was the best for Irbesartan removal, showing a sorption capacity fivefold higher than the NIP. Regarding the adsorption kinetics, the analyte-sorbent equilibrium was reached after about 3 h, and the film diffusion model best fitted the kinetic profile. Selectivity was further demonstrated by testing Losartan, another sartan drug, observing a fourfold lower sorption capacity, but still higher than that of NIP. The polymers were also synthesized in cartridges for solid-phase extraction (SPE), which was helpful for evaluating the breakthrough curves and performing pre-concentrations. These have been done in tap and river water samples (100-250 mL, 15-500 µg L-1 Irbesartan), obtaining quantitative sorption/desorption on the MIP-polyHIPE (RSD < 14%, n = 3). The NIP provided a recovery of just around 30%, evidence of partial uptake of the target from water.

Glycovaccine Design: Optimization of Model and Antitubercular Carrier Glycosylation via Disuccinimidyl Homobifunctional Linker.

Conjugation via disuccinimidyl homobifunctional linkers is reported in the literature as a convenient approach for the synthesis of glycoconjugate vaccines. However, the high tendency for hydrolysis of disuccinimidyl linkers hampers their extensive purification, which unavoidably results in side-reactions and non-pure glycoconjugates. In this paper, conjugation of 3-aminopropyl saccharides via disuccinimidyl glutarate (DSG) was exploited for the synthesis of glycoconjugates. A model protein, ribonuclease A (RNase A), was first considered to set up the conjugation strategy with mono- to tri- mannose saccharides. Through a detailed characterization of synthetized glycoconjugates, purification protocols and conjugation conditions have been revised and optimized with a dual aim: ensure high sugar-loading and avoid the presence of side reaction products. An alternative purification approach based on hydrophilic interaction liquid chromatography (HILIC) allowed the formation of glutaric acid conjugates to be avoided, and a design of experiment (DoE) approach led to optimal glycan loading. Once its suitability was proven, the developed conjugation strategy was applied to the chemical glycosylation of two recombinant antigens, native Ag85B and its variant Ag85B-dm, that are candidate carriers for the development of a novel antitubercular vaccine. Pure glycoconjugates (≥99.5%) were obtained. Altogether, the results suggest that, with an adequate protocol, conjugation via disuccinimidyl linkers can be a valuable approach to produce high sugar-loaded and well-defined glycovaccines.

Effect of mobile phase pH on liquid chromatography retention of mepartricin related compounds and impurities as support to the structural investigation by liquid chromatography-mass spectrometry.

Mepartricin is a semisynthetic polyene macrolide with antifungal and anti-protozoal activities, and it is widely used for the treatment of benign prostatic hyperplasia. Mepartricin is produced by synthetic methyl esterification of the more toxic partricin, and its activity is due to a complex of related compounds. Among them, the main ones are mepartricin B and mepartricin A which are characterized by the presence of a primary and a secondary amine group, respectively. In this work a previously reported HPLC-UV method was properly modified to make it MS-compatible. The selected conditions entail the use of a C18 reverse phase column, and a mobile phase composed by ammonium formate and acetonitrile, with the addition of heptafluorobutyric acid as modifier. The developed method was applied to the characterization of a mepartricin reference standard and a mepartricin experimental batch. All the UV responding peaks, 30 for the standard and 21 for the experimental batch, were successfully detected by MS, allowing to define their m/z values and acquire their fragmentation spectra. For the structural elucidation of isobaric species and, in particular, the identification of toxic partricin-related impurities, the presence of differently ionisable chemical groups was considered, as partricins contain free caboxy-groups, while mepartricins represent their estherified counterparts. A deep study of the effect of mobile phase pH on the chromatographic retention of partricin and mepartricin related compounds was performed in the pH range 2.5-6.5. This study allowed to successfully cluster all the detected species and asses, in the considered batch, the absence of other partricin-related impurities in addition to partricin B and partricin A.

Carbon nanotubes-modified poly-high internal phase emulsions for pharmaceuticals pre-concentration and determination.

This paper deals with the preparation of new composites between polymerized/crosslinked high internal phase emulsions (polyHIPEs) and carbon nanotubes (CNTs), specifically designed for pharmaceutical analytical applications. While the composition of the polyHIPEs was maintained constant, the amount of CNTs was varied from 0.5% to 1% w/v. As proof-of-concept, the materials were tested for solid-phase extraction. Three drugs with different physical-chemical properties, namely 17ß-estradiol (E2), Naproxen (NPX), and Oxprenolol (OXP) were selected as probes to investigate the adsorption/elution conditions on/from the CNT/polyHIPE composites for future analytical applications. The sorption and desorption behavior of the three analytes was studied at different pH values. The experimental results are coherent with chemistry of the support and the physical-chemical characteristics of the considered analytes. The incorporation of CNTs into the polyHIPEs network strongly influences the sorption properties of these materials.

Multi-approach LC-MS methods for the characterization of species-specific attributes of monoclonal antibodies from plants.

In this work, an analytical platform based on the use of chromatography and mass spectrometry (MS), has been applied to the characterization of Rituximab (RTX) obtained from two plant expression systems (rice and tobacco) in comparison to the mammalian cell-derived reference monoclonal antibody (mAb). Different chromatographic approaches, hyphenated to high resolution MS (HRMS), were applied to RTX structural investigation both at middle- and peptide level. In particular, cation exchange chromatography (CEX), size exclusion chromatography (SEC), reversed phase (RPLC) and hydrophilic interaction liquid chromatographic (HILIC) methods were developed and applied on intact mAbs, IdeS-, and trypsin digests in order to address critical attributes such as primary structure, glycan composition, species-related heterogeneity, glycosylation degree, charge variants, aggregation tendency and enzymatic stability. All the collected data highlight the features and criticalities of each production approach. Production in rice results in a heterogeneous but stable product over time, suggesting the absence of proteases in seeds; while tobacco expression system leads to more homogeneous glycosylation, but protein stability seems to be a critical issue probably due to the presence of proteases. This analytical strategy represents a robust support to scientists in the selection and optimization of the best plant expression system to produce recombinant humanized mAbs.

Monolithic Papain-Immobilized Enzyme Reactors for Automated Structural Characterization of Monoclonal Antibodies.

The characterization of monoclonal antibodies (mAbs) requires laborious and time-consuming sample preparation steps before the liquid chromatography-mass spectrometry (LC-MS) analysis. Middle-up approaches entailing the use of specific proteases (papain, IdeS, etc.) emerged as practical and informative methods for mAb characterization. This work reports the development of immobilized enzyme reactors (IMERs) based on papain able to support mAb analytical characterization. Two monolithic IMERs were prepared by the covalent immobilization of papain on different supports, both functionalized via epoxy groups: a Chromolith® WP 300 Epoxy silica column from Merck KGaA and a polymerized high internal phase emulsion (polyHIPE) material synthesized by our research group. The two bioreactors were included in an in-flow system and characterized in terms of immobilization yield, kinetics, activity, and stability using Nα-benzoyl-L-arginine ethyl ester (BAEE) as a standard substrate. Moreover, the two bioreactors were tested toward a standard mAb, namely, rituximab (RTX). An on-line platform for mAb sample preparation and analysis with minimal operator manipulation was developed with both IMERs, allowing to reduce enzyme consumption and to improve repeatability compared to in-batch reactions. The site-specificity of papain was maintained after its immobilization on silica and polyHIPE monolithic supports, and the two IMERs were successfully applied to RTX digestion for its structural characterization by LC-MS. The main pros and cons of the two supports for the present application were described.

Design of epidermal growth factor immobilization on 3D biocompatible scaffolds to promote tissue repair and regeneration.

Exogenous application of human epidermal growth factor (hEGF) stimulates epidermal wound healing. The aim of this study was to develop bioconjugates based on hEGF mimicking the protein in its native state and thus suitable for tissue engineering applications, in particular for treating skin-related disorders as burns. Ribonuclease A (RNase A) was used to investigate a number of different activated-agarose carriers: cyanogen bromide (CNBr)-activated-agarose and glyoxyl-agarose showed to preserve the appropriate orientation of the protein for receptor binding. EGF was immobilized on these carriers and immobilization yield was evaluated (100% and 12%, respectively). A peptide mapping of unbound protein regions was carried out by LC-MS to take evidence of the residues involved in the immobilization and, consequently, the flexibility and surface accessibility of immobilized EGF. To assess cell proliferative activities, 10, 25, 50, and 100 ng/mL of each immobilized EGF sample were seeded on fibroblast cells and incubated for 24, 48 and 72 h. The immobilized growth factor showed significantly high cell proliferative activity at 50 and 100 ng/mL compared to control and soluble EGF. Although both of the immobilized samples show dose-dependency when seeded with high number of fibroblast cells, CNBr-agarose-EGF showed a significantly high activity at 100 ng/mL and 72 h incubation, compared to glyoxyl-agarose-EGF.

Discovery of a Novel Inhibitor of Human Purine Nucleoside Phosphorylase by a Simple Hydrophilic Interaction Liquid Chromatography Enzymatic Assay.

Human purine nucleoside phosphorylase (HsPNP) belongs to the purine salvage pathway of nucleic acids. Genetic deficiency of this enzyme triggers apoptosis of activated T-cells due to the accumulation of deoxyguanosine triphosphate (dGTP). Therefore, potential chemotherapeutic applications of human PNP inhibitors include the treatment of T-cell leukemia, autoimmune diseases and transplant tissue rejection. In this report, we present the discovery of novel HsPNP inhibitors by coupling experimental and computational tools. A simple, inexpensive, direct and non-radioactive enzymatic assay coupled to hydrophilic interaction liquid chromatography and UV detection (LC-UV using HILIC as elution mode) was developed for screening HsPNP inhibitors. Enzymatic activity was assessed by monitoring the phosphorolysis of inosine (Ino) to hypoxanthine (Hpx) by LC-UV. A small library of 6- and 8-substituted nucleosides was synthesized and screened. The inhibition potency of the most promising compound, 8-aminoinosine (4), was quantified through Ki and IC50 determinations. The effect of HsPNP inhibition was also evaluated in vitro through the study of cytotoxicity on human T-cell leukemia cells (CCRF-CEM). Docking studies were also carried out for the most potent compound, allowing further insights into the inhibitor interaction at the HsPNP active site. This study provides both new tools and a new lead for developing novel HsPNP inhibitors.

Proteomic analysis of small acid soluble proteins in the spore core of Bacillus subtilis ΔprpE and 168 strains with predictions of peptides liquid chromatography retention times as an additional tool in protein identification.

BACKGROUND: Sporulation, characteristic for some bacteria such as Bacillus subtilis, has not been entirely defined yet. Protein phosphatase E (PrpE) and small, acid soluble spore proteins (SASPs) influence this process. Nevertheless, direct result of PrpE interaction on SASPs content in spore coat of B. subtilis has not been evidenced so far. As proteomic approach enables global analysis of occurring proteins, therefore it was chosen in this experiment to compare SASPs occurrence in two strains of B. subtilis, standard 168 and ΔprpE, lacking PrpE phosphatase. Proteomic analysis is still a challenge, and despite of big approach in mass spectrometry (MS) field, the identification reliability remains unsatisfactory. Therefore there is a rising interest in new methods, particularly bioinformatic tools that would harden protein identification. Most of currently applied algorithms are based on MS-data. Information from separation steps is not still in routine usage, even though they also provide valuable facts about analyzed structures. The aim of this research was to apply a model for peptides retention times prediction, based on quantitative structure-retention relationships (QSRR) in SASPs analysis, obtained from two strains of B. subtilis proteome digests after separation and identification of the peptides by LC-ESI-MS/MS. The QSRR approach was applied as the additional constraint in proteomic research verifying results of MS/MS ion search and confirming the correctness of the peptides identifications along with the indication of the potential false positives and false negatives. RESULTS: In both strains of B. subtilis, peptides characteristic for SASPs were found, however their identification confidence varied. According to the MS identity parameter Xcorr and difference between predicted and experimental retention times (ΔtR) four groups could be distinguished: correctly and incorrectly identified, potential false positives and false negatives. The ΔprpE strain was characterized by much higher amount of SASPs peptides than standard 168 and their identification confidence was, mostly for alpha- and beta-type SASP, satisfactory. CONCLUSIONS: The QSRR-based model for predicting retention times of the peptides, was a useful additional to MS tool, enhancing protein identification. Higher content of SASPs in strain lacking PrpE phosphatase suggests that this enzyme may influence their occurrence in the spores, lowering levels of these proteins.

Correctness of protein identifications of Bacillus subtilis proteome with the indication on potential false positive peptides supported by predictions of their retention times.

The predictive capability of the retention time prediction model based on quantitative structure-retention relationships (QSRR) was tested. QSRR model was derived with the use of set of peptides identified with the highest scores and originated from 8 known proteins annotated as model ones. The predictive ability of the QSRR model was verified with the use of a Bacillus subtilis proteome digest after separation and identification of the peptides by LC-ESI-MS/MS. That ability was tested with three sets of testing peptides assigned to the proteins identified with different levels of confidence. First, the set of peptides identified with the highest scores achieved in the search were considered. Hence, proteins identified on the basis of more than one peptide were taken into account. Furthermore, proteins identified on the basis of just one peptide were also considered and, depending on the possessed scores, both above and below the assumed threshold, were analyzed in two separated sets. The QSRR approach was applied as the additional constraint in proteomic research verifying results of MS/MS ion search and confirming the correctness of the peptides identifications along with the indication of the potential false positives.