Capillary electrophoresis of large cyanogen bromide peptides of fibre-forming collagens with special reference to cross-linking

Peptide mapping of proteins by capillary electromigration methods

This review article provides a wide overview of important developments and applications of capillary electromigration methods in the area of peptide mapping of proteins in the period 1997-mid-2022, including review articles on this topic. It deals with all major aspects of peptide mapping by capillary electromigration methods: i) precleavage sample preparation involving purification, preconcentration, denaturation, reduction and alkylation of protein(s) to be analyzed, ii) generation of peptide fragments by off-line or on-line enzymatic and/or chemical cleavage of protein(s), iii) postcleavage preparation of the generated peptide mixture for capillary electromigration separation, iv) separation of the complex peptide mixtures by one-, two- and multidimensional capillary electromigration methods coupled with mass spectrometry detection, and v) a large application of peptide mapping for variable purposes, such as qualitative analysis of monoclonal antibodies and other protein biopharmaceuticals, monitoring of posttranslational modifications, determination of primary structure and investigation of function of proteins in biochemical and clinical research, characterization of proteins of variable origin as well as for protein and peptide identification in proteomic and peptidomic studies.

Capillary electromigration methods for the study of collagen

This review paper gives an overview of capillary electromigration methods used in the analysis of collagen. Analyses of the parent chains as well as of the bromcyane and collagenase fragments of collagens are presented. Methods include capillary zone electrophoresis, capillary gel electrophoresis, micellar electrokinetic chromatography as well as combinations of HPLC and capillary electrophoresis, and capillary electrophoresis with mass spectrometry.

Quantitative measurement of collagen methylation by capillary electrophoresis

Collagen methylation has been exploited in various applications involving living cells. We have observed correlation between the collagen methylation with the rate of cell proliferation in three-dimensional (3-D) microenvironment. To quantify the degree of collagen methylation, we have developed a capillary zone electrophoresis method. Using a polyvinyl alcohol-coated fused-silica capillary and UV detection at 200 nm, we have optimized pH and separated the native collagen into three major bands in phosphate buffer (50 mM, pH 2.5) with 0.05% hydroxypropylmethylcellulose. Under these conditions, the methylated collagens were separated into four major bands, which changed with different methylation reaction conditions. We propose an index to quantify the degree of collagen methylation that also correlates with their effects on cell proliferation.

Separation of structurally related synthetic peptides by capillary zone electrophoresis

The separation of two different sets of synthetic peptides has been investigated by high-performance capillary zone electrophoresis utilising naked, fused silica capillaries. The effects of electrolyte pH, buffer concentration, capillary length and electric field strength on the separation efficiency and selectivity were systematically varied, with the highest resolution achieved with buffer electrolytes of low pH and relatively high ionic strength. Under optimised separation conditions utilising the "short end injection" separation approach with negative electric field polarity, a series of eight structurally-related synthetic peptides were baseline resolved within 4 min without addition of any modifier of the background electrolyte with separation efficiencies in the vicinity of 600000 theoretical plates/m. Further significant enhancement of separation efficiencies could be achieved by taking advantage of the "long end injection" approach with positive electric field polarity. The outcome of these experimental variations parallels the "sweeping" effect that has been observed in the capillary electrochromatographic and micellar electrokinetic separations of polar molecules and permits rapid resolution of peptides with focusing effects. In addition, small changes in the electrolyte buffer pH and concentration were found to have a significant impact on the selectivity of synthetic peptides of similar intrinsic charge. These observations indicate that multi-modal separation mechanisms operated under these conditions with the unmodified fused silica capillaries. This study, moreover, documents additional examples of peptide-specific multi-zoning behaviour in the high-performance capillary zone electrophoretic separation of synthetic peptides.

Preparative procedures and purity assessment of collagen proteins

Collagens represent a large family (25 members identified so far) of closely related proteins. While the preparative procedures for the members that are ubiquitous and present in tissues in large quantities (typically fibre and network forming collagens types I, II, III, IV and V) are well established, the procedures for more recently discovered minor collagen types, namely those possessing large non-collagenous domain(s) in their molecule, are mostly micropreparative and for some collagenous proteins even do not exist. The reason is that the proof of their existence is based on immunochemical staining of tissue slices and nucleic database searching. Methods of preparation and identification of constituting alpha-polypeptide chains as well as collagenous and non-collagenous domains are also reviewed. Methods for revealing non-enzymatic posttranslational modifications (particularly of the fibre forming collagen types) are briefly described as well.

Evaluation of peptide electropherograms by multivariate mathematical-statistical methods. I. Principal component analysis

Depository effects in slowly metabolised proteins, typically glycation or the estimation of products arising from the reaction of unsaturated long-chain-fatty acid metabolites (possessing aldehydic groups) are very difficult to assess owing to their extremely low concentration in the protein matrix. In order to reveal such alterations we applied deep enzymatic fragmentation resulting in a set of small peptides, which, if modified, are likely to change their electrophoretic properties and can be visualised on the resulting profile. Peptide maps of collagen (a mixture of collagen types I and III digested by bacterial collagenase) were applied as the model protein structure for detecting the nonenzymatic posttranslational changes originating during various physiological conditions like high fructose diet and hypertriglyceridemic state. Capillary electrophoresis in acidic media (sodium phosphate buffer, pH 2.5) was used as the separation method capable of (partial) separation of over 60 peptide peaks. Two to 13 changes were revealed in the profiles obtained reflecting the physiological conditions of the animals tested. Combination of peptide profiling with subsequent t-test evaluation of individual peak areas and principal component analysis based on cumulative peak areas of individual sections of the electropherograms allowed to determine in which section (part) of the electropherogram the physiological state indicating changes occurred. Simultaneously it was possible to reveal the qualitative differences between the four physiological regimes investigated (i.e., which regime affects the collagen molecules most and which affects them least). The approach can be used as guidance for targeted preseparation of the very complex peptide mixture.

Capillary electrophoretic separation of proteins and peptides using Pluronic liquid crystals and surface-modified capillaries

Separation of model mixtures of peptides/proteins carried out in a hydrophilically coated capillary in 10 mmol/l Tris and 75 mmol/l phosphate buffer containing 7.5% (w/w) Pluronic F127 copolymer (apparent pH 2.9) revealed that the separation is predominantly driven by the charge/mass ratio with little or no sieving effect. Using a coated capillary helped to remove current fluctuations that are observed in the fused-silica capillaries in the presence of the Pluronic copolymer. With peptides bearing distinct positive charge (polylysine of Mr around 3300) molecular sieving helps more detailed separation of individual species. Polyamino acids carrying negative charge can be brought to the detector window in the reversed polarity mode, however, no detailed separation of the individual species involved was observed under the conditions used. With a naturally occurring mixture of collagen fragments released by CNBr treatment of the protein the sequence of emerging peptides (positive polarity mode) with no relation to the rel. mol. mass could be revealed. It is concluded that separation of proteins/peptides in the presence of Pluronic in the background electrolyte occur on the charge/mass ratio basis with molecular sieving effects acting as a secondary partition mechanism.

Application of Pluronic copolymer liquid crystals for the capillary electrophoretic separation of collagen type I cyanogen bromide fragments

A capillary electrophoretic method exploiting the properties of Pluronic copolymer liquid crystals (F127) was developed for the separation of collagen cyanogen bromide (CNBr) fragments. The separations obtained were at least comparable (if not better) to those obtained by other methods applicable to this category of compounds. In the optimized version a bare silica capillary [47 cm (40 cm to the detector) x 75 microm I.D.] was used with 10 mM Tris and 75 mM phosphate buffer (pH 2.5) containing 7.5% Pluronic F127 copolymer. The separation mechanism which involves both the molecular sieving and surfactant properties of the Pluronic F127 gel phase is discussed.

Capillary electrophoresis of peptides

This article gives a review of the recent developments in capillary electrophoresis (CE) of peptides. New approaches to the theoretical description of electromigration behavior of peptides are described, and methodological aspects of CE separations of peptides such as selection of separation conditions, sample treatment, suppression of peptide adsorption to the capillary wall and specificities of CE separation modes are discussed. Progress in application of high performance detection schemes, namely laser-induced fluorescence and mass spectrometry, in peptide separations by CE is presented. Applications of different CE techniques, zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography and electrochromatography to peptide analysis, preparation and physicochemical characterization are demonstrated.

Micropreparation of tissue collagenase fragments of type I collagen in the form of surfactant-peptide complexes and their identification by capillary electrophoresis and partial sequencing

Combination of standard approaches like pepsin digestion and slab gel electrophoresis with capillary separations allows a relatively easy identification of in vivo occurring collagen fragments. Capillary electrophoresis can be done either in 25 mM phosphate buffer (pH 2.5) or in a 25 mM phosphate buffer (pH 4.5) made 0.1% with respect to sodium dodecyl sulfate (SDS). While in the first case peptides move to the cathode in a molecular mass dependent manner, in the second case they move towards anode (also in a molecular mass dependent manner). The profiles obtained by the two approaches resemble mirror images with low molecular mass peptides moving first in the acid background electrolyte while they move last in the presence of SDS. It is proposed that in the capillary electrophoretic separation at pH 2.5 the separation mechanism involves the interaction of the individual peptides with the capillary wall while in the second case (pH 4.5) the leading mechanism of separation involves the interaction of the analytes with the micellar phase. For micellar phase separation the system must be run at reversed polarity. Capillary electrophoretic separation in the pH 2.5 buffer is considerably affected by the presence of SDS in the previous steps of peptide preparation. If the peptides are obtained from SDS slab gel electrophoresis, their movement in the capillary electrophoresis step is about three times faster that the movement of corresponding peptides which have not been complexed with SDS.

Post-translational non-enzymatic modification of proteins. II. Separation of selected protein species after glycation and other carbonyl-mediated modifications

There are two strategies applicable to revealing non-enzymatic post-translational modifications of proteins; while assaying of the hydrolytically stable adducts was the subject of our previous communication [1], here we attempted to review separation technologies for the unfragmented modified proteins. There are a few standard procedures used for this purpose, namely Laemmli gel electrophoresis, different modes of gel permeation chromatography and boronate affinity chromatography. The latter approach makes use of the vicinal hydroxy groups present in glycated proteins. Some (but not all) arising adducts exhibit typical fluorescence which can be exploited for detection. In most cases fluorescence is measured at 370/440 nm for the so-called advanced glycation products or at 335/385 nm for the only so far well characterized glycation marker (pentosidine). Some indication exists that, e.g., synchronous fluorescence detection will probably in the future add to the selectivity and allow the distinction of the different adducts arising during non-enzymatic post-translational modifications (glycation). The proteins reviewed are serum albumin, collagen and lens proteins while glycation of hemoglobin is the subject of another review within the present volume.