Thin layer chromatography of peptides and proteins: a review

High-Performance Thin-Layer Chromatography-Immunostaining as a Technique for the Characterization of Whey Protein Enrichment in Edam Cheese

Whey protein-enriched cheese can be produced by means of a high-temperature treatment of a part of the cheese milk. In this way, the nutritional quality of the resulting cheeses can be increased while resources are conserved. High-performance thin-layer chromatography-immunostaining (HPTLC-IS) using specific β-lactoglobulin (β-LG) antibodies was applied to study the implementation and stability of β-LG in two different sample sets of whey protein-enriched Edam model cheeses, including industrial-scale ones. Two methods were compared for the extraction of the proteins/peptides from the cheese samples. By applying tryptic hydrolysis directly from a suspended cheese sample instead of a supernatant of a centrifuged suspension, a better yield was obtained for the extraction of β-LG. When applying this method, it was found that selected epitopes in the tryptic β-LG peptides remain stable over the ripening period of the cheese. For four of the tryptic β-LG peptides detected by immunostaining, the amino acid sequence was identified using MALDI-TOF-MS/MS. One of the peptides identified was the semi-tryptic peptide VYVEELKPTP. A linear relationship was found between the content of this peptide in cheese and the proportion of high-heated milk in the cheese milk. β-LG enrichment factors of 1.72 (n = 3, sample set I) and 1.33 ± 0.19 (n = 1, sample set II) were determined for the cheese samples containing 30% high-heated milk compared to the non-enriched samples. The relative β-LG contents in the cheese samples with 30% high-heated milk were calculated to be 4.35% ± 0.39% (sample set I) and 9.11% ± 0.29% (sample set II) using a one-point calibration. It can be concluded that the HPTLC-IS method used is a suitable tool for the analysis of whey protein accumulation in cheese, being therefore potentially directly applicable on an industrial scale. For more accurate quantification of the whey protein content in cheese, an enhanced calibration curve needs to be applied.

Two-dimensional high-performance thin-layer chromatography for the characterization of milk peptide properties and a prediction of the retention behavior - a proof-of-principle study

High-performance thin-layer chromatography (HPTLC) is a suitable method for the analysis of peptides and proteins due to a wide selection of stationary and mobile phases and various detection options. Especially, two-dimensional HPTLC (2D-HPTLC) enables a higher resolution compared to one-dimensional HPTLC in the separation of complex peptide mixtures. Similar to 2D electrophoresis, characteristic peptide patterns can be obtained, allowing a differentiation of ingredients based on varying protein origins. The aim of this study was to evaluate 2D-HPTLC with regard to its suitability for the characterization of proteins/peptides and to verify whether it is possible to predict the retention behavior of peptides based on their properties. As models, the five most abundant milk proteins α-lactalbumin, β-lactoglobulin, α-, β-, and κ-Casein were used. In order to determine the repeatability of the peptide separation by 2D-HPTLC, each tryptic protein hydrolyzate was separated eight times. The standard deviations of the retardation factors for the separated peptides varied between 1.0 and 11.1 mm for the x-coordinate and 0.5-7.3 mm for the y-coordinate. It was also shown that after the chromatographic separation, peptides of the individual protein hydrolyzates were located in specific areas on the HPTLC plate, so that a clustering could be obtained for the whey proteins' as well as the caseins' hydrolyzates. For establishing correlations between the properties of the peptides and their retardation factors, 51 of 85 selected peptides were identified by matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF-MS/MS). On this basis, statistically significant correlations (α = 0.05) between the retardation factors of the peptides and their isoelectric points, as well as the percentage of anionic and non-polar amino acids in the peptides were established. Finally, it was investigated, whether the retardation factors for peptides can be predicted on the basis of a linear regression of the percentage of non-polar amino acids in a peptide. For this purpose, a mixture of artifical (synthetic) peptides (n = 14) was separated by 2D-HPTLC and the measured retardation factors were compared with the corresponding retardation factors calculated. Absolute deviations of 0.3-17.9 mm were obtained. In addition, the universal applicability of the method to other protein sources other than milk proteins (animal protein) was tested using a mixture of pea peptides (plant protein, n = 3) resulting in absolute deviations of 0.7-8.6 mm.

Asian hornet Vespa velutina nigrithorax venom: Evaluation and identification of the bioactive compound responsible for human keratinocyte protection against oxidative stress

The present study aimed to explore the potential antioxidant molecules of the Asian hornet venom (Vespa velutina nigrithorax) responsible for radical scavenging activity and human keratinocyte protection against oxidative stress. We developed a first technical platform that combined a DPPH radical scavenging chemical assay and cytotoxicity and ROS (reactive oxygen species) production in HaCaT keratinocyte cells exposed to UVB to evaluate the antioxidant property of V. velutina venom. We further employed Thin Layer Chromatography (TLC) combined with the DPPH assay as a targeted separation approach to isolate the antioxidant compounds responsible for the free radical scavenging property of V. velutina venom. In parallel, the latter was fractionated by a HPLC-DAD non-targeted separation approach. From this experiment, nine fractions were generated which were again evaluated separately for their antioxidant properties using DPPH assays. Results showed that only one fraction exhibited significant antioxidant activity in which serotonin was identified as the major compound by a UHPLC-ESI-QTOF HRMS/MS approach. We finally demonstrated, using purified serotonin molecule that this bioactive structure is mostly responsible for the free radical scavenging property of the crude venom as evidenced by DPPH and ROS assays in HaCaT cells exposed to UVB.

Isolation and Identification of Dipeptidyl Peptidase IV-Inhibitory Peptides from Trypsin/Chymotrypsin-Treated Goat Milk Casein Hydrolysates by 2D-TLC and LC-MS/MS

New dipeptidyl peptidase IV (DPP-IV)-inhibitory peptides from trypsin/chymotrypsin-treated goat milk casein hydrolysates were isolated and identified by two-dimensional silica thin-layer chromatography (2D-TLC) combined to nano LC-MS/MS. 2D-TLC with chloroform/methanol/25% ammonia (2:2:1) and n-butanol/acetic acid/water (4:1:1) as the first- and second-dimension eluents, respectively, in analytical and semipreparative scales, was set up and verified by reversed-phase high-performance liquid chromatography (RP-HPLC) to be feasible and efficient to separate the hydrolysates. Five new DPP-IV-inhibitory peptides, four relatively large oligopeptides (MHQPPQPL, SPTVMFPPQSVL, VMFPPQSVL, and INNQFLPYPY), and AWPQYL were identified, and INNQFLPYPY showed a notable IC50 value of 40.08 μM as an uncompetitive inhibitor. Interactive effects on DPP-IV inhibition were also observed among separated fractions and pure synthetic peptide mixtures with concentration-dependent activity. The study gives new insights into goat casein hydrolysates with identified DPP-IV-inhibitory peptides efficiently isolated by 2D-TLC, which provides a simple and cost-efficient separation process and is compatible with liquid chromatography-tandem mass spectrometry (LC-MS/MS) identification.

Antihypertensive effect of the bovine casein-derived peptide Met-Lys-Pro

The antihypertensive effect of the bovine casein-derived peptide Met-Lys-Pro (MKP) was examined in vitro and in vivo. MKP showed angiotensin I-converting enzyme (ACE)-inhibitory activity in vitro (IC50 = 0.43 μM). An in vivo kinetics study using radiolabeled Met-[1-(14)C]Lys-Pro ((14)C-MKP) showed that orally administered (14)C-MKP to spontaneously hypertensive rats (SHRs) was absorbed and moved into the plasma. In vitro vasoconstriction of thoracic aorta preparations, which was induced by adding angiotensin I, was reduced by prior exposure of MKP. A single oral dose of MKP lowered systolic blood pressure (SBP) of SHRs, and repeated oral administration of MKP for 28 days significantly lowered SBP of SHRs. The results obtained in the present study suggest that orally administrated MKP can be absorbed into the plasma and its ACE-inhibitory activity may contribute to induce the antihypertensive effect in vivo.

Protein UTLC-MALDI-MS using thin films of submicrometer silica particles

Slides for ultra thin-layer chromatography (UTLC) were made by coating nonporous silica particles, chemically modified with polyacrylamide, as 15 μm films on glass or silicon. Three proteins, myoglobin, cytochrome c and lysozyme, are nearly baseline resolved by the mechanism of hydrophilic interaction chromatography. A plate height as low as 3 μm, with 3900 plates, is observed in 14 mm. Varying silica particle diameter among 900, 700 and 350 nm showed that decreasing particle diameter slightly improves resolution but slows the separation. Matrix-assisted laser desorption/ionization (MALDI)-MS of the proteins after separation is demonstrated by wicking sufficient sinapinic acid into the separation medium.

Separation of peptides on Empore thin-layer chromatography sheets and blotting onto polyvinylidene difluoride membranes with subsequent gas phase sequencing

Methods for the separation of peptides on a new type of thin-layer chromatography (TLC) sheet and blotting onto polyvinylidene difluoride (PVDF) membranes with subsequent gas phase sequencing are described. For validation, the A and B chain of insulin were chromatographed on Empore TLC sheets and either extracted or blotted onto PVDF membranes. The advantages and disadvantages of thin-layer chromatography on Empore sheets versus high performance liquid chromatography (HPLC) are discussed, along with the possibility of combining the two methods. In addition, TLC was combined with electrophoresis (fingerprinting) for the separation of complex peptide mixtures. Blotting from TLC sheets onto PVDF membranes was performed in two ways: contact diffusion and electrophoretic transfer. In our experiments electroblotting was more effective. Amino acid sequence determination of the B chain of insulin was possible both after extraction from the TLC sheet and after blotting onto PVDF membranes. In the former case, liquid phase sequencing and, in the latter case, gas phase sequencing was performed. The possibility to blot from TLC sheets onto membranes, e.g. PVDF, may prove useful in many fields, for example in biochemistry, and in molecular and cell biology.

Thin layer chromatography of dansyl and dinitrophenyl derivatives of amino acids. A review

The dinitrophenyl (DNP) derivatives of amino acids have found continual application in protein sequencing since Sanger used them for the first time for the sequencing of insulin. Dansyl derivatives of amino acids have been widely used in protein sequencing because of their fluorescent nature. The success of protein sequencing largely depends upon correct identification of such derivatives. The choice for the method of identification is related to cost, the availability of instrumentation and to the sensitivity needed for the analysis. Thin layer chromatography (TLC) is simple and has several advantages over other chromatographic methods. Therefore the literature after 1972 is reviewed for TLC analysis of dansyl- and DNP-amino acids, the two important amino acid derivatives required for identifying protein sequences. Additionally, the literature on the TLC resolution of enantiomeric mixtures of dansyl amino acids is reviewed. Application of various adsorbents, composition of solvent systems and other experimental conditions together with successful resolution data have been discussed. TLC provides a direct and inexpensive method for the resolution of enantiomers, and is fast becoming a sensitive instrumentalized quantitative analytical technique.