Advances in the separation, sensitive detection, and characterization of heparin and heparan sulfate

Proteoglycomics: recent progress and future challenges

Proteoglycomics is a systematic study of structure, expression, and function of proteoglycans, a posttranslationally modified subset of a proteome. Although relying on the established technologies of proteomics and glycomics, proteoglycomics research requires unique approaches for elucidating structure-function relationships of both proteoglycan components, glycosaminoglycan chain, and core protein. This review discusses our current understanding of structure and function of proteoglycans, major players in the development, normal physiology, and disease. A brief outline of the proteoglycomic sample preparation and analysis is provided along with examples of several recent proteoglycomic studies. Unique challenges in the characterization of glycosaminoglycan component of proteoglycans are discussed, with emphasis on the many analytical tools used and the types of information they provide.

Applications of isotopes in advancing structural and functional heparanomics

Heparanomics is the study of all the biologically active oligosaccharide domain structures in the entire heparanome and the nature of the interactions among these domains and their protein ligands. Structural elucidation of heparan sulfate and heparin oligosaccharides is a major obstacle in advancing structure-function relationships and heparanomics. There are several factors that exacerbate the challenges involved in the structural elucidation of heparin and heparan sulfate; therefore, there is great interest in developing novel strategies and analytical tools to overcome the barriers in decoding the enigmatic heparanome. This review focuses on the applications of isotopes, both radioisotopes and stable isotopes, in the structural elucidation of the complex heparanome at the disaccharide or oligosaccharide level using liquid chromatography, nuclear magnetic resonance spectroscopy, and mass spectrometry. This review also outlines the utility of isotopes in determining the substrate specificity of biosynthetic enzymes that eventually dictate the emergence of biologically active oligosaccharides.

Analysis and characterization of heparin impurities

This review discusses recent developments in analytical methods available for the sensitive separation, detection and structural characterization of heparin contaminants. The adulteration of raw heparin with oversulfated chondroitin sulfate (OSCS) in 2007–2008 spawned a global crisis resulting in extensive revisions to the pharmacopeia monographs on heparin and prompting the FDA to recommend the development of additional physicochemical methods for the analysis of heparin purity. The analytical chemistry community quickly responded to this challenge, developing a wide variety of innovative approaches, several of which are reported in this special issue. This review provides an overview of methods of heparin isolation and digestion, discusses known heparin contaminants, including OSCS, and summarizes recent publications on heparin impurity analysis using sensors, near-IR, Raman, and NMR spectroscopy, as well as electrophoretic and chromatographic separations.

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Characterization of uniformly and atom-specifically (13)C-labeled heparin and heparan sulfate polysaccharide precursors using (13)C NMR spectroscopy and ESI mass spectrometry

The biological actions of heparin and heparan sulfate, two structurally related glycosaminoglycans, depend on the organization of the complex heparanome. Due to the structural complexity of the heparanome, the sequence of variably sulfonated uronic acid and glucosamine residues is usually characterized by the analysis of smaller oligosaccharide and disaccharide fragments. Even characterization of smaller heparin and heparan sulfate oligosaccharide or disaccharide fragments using simple 1D (1)H NMR spectroscopy is often complicated by the extensive signal overlap. (13)C NMR signals, on the other hand, overlap less and therefore, (13)C NMR spectroscopy can greatly facilitate the structural elucidation of the complex heparanome and provide finer insights into the structural basis for biological functions. This is the first report of the preparation of anomeric carbon-specific (13)C-labeled heparin and heparan sulfate precursors from the Escherichia coli K5 strain. Uniformly (13)C- and (15)N-labeled precursors were also produced and characterized by (13)C NMR spectroscopy. Mass spectrometric analysis of enzymatically fragmented disaccharides revealed that anomeric carbon-specific labeling efforts resulted in a minor loss/scrambling of (13)C in the precursor backbone, whereas uniform labeling efforts resulted in greater than 95% (13)C isotope enrichment in the precursor backbone. These labeled precursors provided high-resolution NMR signals with great sensitivity and set the stage for studying the heparanome-proteome interactions.

Heparin-derived heparan sulfate mimics to modulate heparan sulfate-protein interaction in inflammation and cancer

The heparan sulfate (HS) chains of heparan sulfate proteoglycans (HSPG) are "ubiquitous" components of the cell surface and the extracellular matrix (EC) and play important roles in the physiopathology of developmental and homeostatic processes. Most biological properties of HS are mediated by interactions with "heparin-binding proteins" and can be modulated by exogenous heparin species (unmodified heparin, low molecular weight heparins, shorter heparin oligosaccharides and various non-anticoagulant derivatives of different sizes). Heparin species can promote or inhibit HS activities to different extents depending, among other factors, on how closely their structure mimics the biologically active HS sequences. Heparin shares structural similarities with HS, but is richer in "fully sulfated" sequences (S domains) that are usually the strongest binders to heparin/HS-binding proteins. On the other hand, HS is usually richer in less sulfated, N-acetylated sequences (NA domains). Some of the functions of HS chains, such as that of activating proteins by favoring their dimerization, often require short S sequences separated by rather long NA sequences. The biological activities of these species cannot be simulated by heparin, unless this polysaccharide is appropriately chemically/enzymatically modified or biotechnologically engineered. This mini review covers some information and concepts concerning the interactions of HS chains with heparin-binding proteins and some of the approaches for modulating HS interactions relevant to inflammation and cancer. This is approached through a few illustrative examples, including the interaction of HS and heparin-derived species with the chemokine IL-8, the growth factors FGF1 and FGF2, and the modulation of the activity of the enzyme heparanase by these species. Progresses in sequencing HS chains and reproducing them either by chemical synthesis or semi-synthesis, and in the elucidation of the 3D structure of oligosaccharide-protein complexes, are paving the way for rational approaches to the development of HS-inspired drugs in the field of inflammation and cancer, as well in other therapeutic fields.

High-resolution preparative separation of glycosaminoglycan oligosaccharides by polyacrylamide gel electrophoresis

Separation of milligram amounts of heparin oligosaccharides ranging in degree of polymerization from 4 to 32 is achieved within 6h using continuous elution polyacrylamide gel electrophoresis (CE-PAGE) on commercially available equipment. The purity and structural integrity of CE-PAGE-separated oligosaccharides are confirmed by strong anion exchange high-pressure liquid chromatography, electrospray ionization Fourier transform mass spectrometry, and two-dimensional nuclear magnetic resonance spectroscopy. The described method is straightforward and time-efficient, affording size-homogeneous oligosaccharides that can be used in sequencing, protein binding, and other structure-function relationship studies.

Human antibodies to herpes simplex virus type 1 glycoprotein C are neutralizing and target the heparan sulfate-binding domain

Human antibodies specific for glycoprotein C (gC1) of herpes simplex virus type 1 (HSV-1) neutralized the virus infectivity and efficiently inhibited attachment of HSV-1 to human HaCaT keratinocytes and to murine mutant L cells expressing either heparan sulfate or chondroitin sulfate at the cell surface. Similar activities were observed with anti-gC1 monoclonal antibody B1C1. In addition to HaCaT and L cells, B1C1 antibody neutralized HSV-1 infectivity in simian GMK AH1 cells mildly pre-treated with heparinase III. Human anti-gC1 antibodies efficiently competed with the binding of gC1 to B1C1 antibody whose epitope overlaps a part of the attachment domain of gC1. Human anti-gC1 and B1C1 antibodies extended survival time of mice experimentally infected with HSV-1. We conclude that in HaCaT cells and in cell systems showing restricted expression of glycosaminoglycans, human and some monoclonal anti-gC1 antibodies can target the cell-binding domain of this protein and neutralize viral infectivity.

Insights into the capillary electrophoresis separation of heparin disaccharides from nuclear magnetic resonance, pKa, and electrophoretic mobility measurements

Determination of the pK(a) values of heparin disaccharide functional groups can provide insights into the nature of glycosaminoglycan (GAG)-protein interactions and prove useful for optimization of the charged-based separations typically used in GAG analysis. In order to gain a better understanding into the capillary electrophoresis (CE) separation process, the pK(a) values of the carboxylate and primary amine moieties of 11 heparin disaccharide standards were determined through (1)H NMR detected pH titrations. These pK(a) values were used to calculate the effective net charge of each disaccharide and compared to the electrophoretic mobilities measured by CE. Although a different migration order had been reported by other researchers, our results indicate a strong positive correlation between the two measurements, consistent with the migration order observed in our CE separations. The effect of mutarotation was also examined by (1)H NMR. Mutarotation equilibrium constants favored the alpha anomer over the beta conformation. pK(a) values determined for both anomers of the four disaccharide standards containing a GlcN primary amine indicated that the beta anomer of the GlcN residue was more acidic. Partial separation of these anomers was achieved in CE separations using either formic acid or phosphate buffer.

Interactions between heparan sulfate and proteins-design and functional implications

Heparan sulfate (HS) proteoglycans at cell surfaces and in the extracellular matrix of most animal tissues are essential in development and homeostasis, and variously implicated in disease processes. Functions of HS polysaccharide chains depend on ionic interactions with a variety of proteins including growth factors and their receptors. Negatively charged sulfate and carboxylate groups are arranged in various types of domains, generated through strictly regulated biosynthetic reactions and with enormous potential for structural variability. The level of specificity of HS-protein interactions is assessed through binding experiments in vitro using saccharides of defined composition, signaling assays in cell culture, and targeted disruption of genes for biosynthetic enzymes followed by phenotype analysis. While some protein ligands appear to require strictly defined HS structure, others bind to variable saccharide domains without any apparent dependence on distinct saccharide sequence. These findings raise intriguing questions concerning the functional significance of regulation in HS biosynthesis.