Infrared spectroscopy of heparins suggests that the region 750-950 cm-1 is sensitive to changes in iduronate residue ring conformation.
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ABSTRACT:
SUBMITTER: Grant D
PROVIDER: S-EPMC1150032 | biostudies-other | 1991 Apr
REPOSITORIES: biostudies-other
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Project description:Analysis by i.r. spectroscopy of natural and chemically modified heparins suggests that the N-sulphonate group of these polymers may vibrationally absorb radiation at two distinctly different frequencies. This property may reflect the existence of different conformational states important in the biological activities of the polymers. Examination of carboxylate- and N-acetyl-group absorbances of these polymers accords with the possibility that one of these polymer conformational states involves interaction between juxtaposed N-sulphonate and carboxylate groups. In heparin bearing large quantities of artificially introduced N-acetyl groups, an interaction between carboxylate and N-acetyl groups may also occur.
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Project description:Mammalian sulphatases (EC 3.1.6) are a family of enzymes that have a high degree of similarity in amino acid sequence, structure and catalytic mechanism. IDS (iduronate-2-sulphatase; EC 3.1.6.13) is a lysosomal exo-sulphatase that belongs to this protein family and is involved in the degradation of the glycosaminoglycans heparan sulphate and dermatan sulphate. An IDS deficiency causes the lysosomal storage disorder MPS II (mucopolysaccharidosis type II). To examine the structural alterations in heat-denatured and mutant IDS, a panel of four monoclonal antibodies was raised to the denatured protein and used as probes of protein conformation. The linear sequence epitope reactivity of a polyclonal antibody raised against the native protein and the monoclonal antibodies were defined and mapped to distinct regions on the IDS protein. The antigenicity of native IDS was higher in regions without glycosylation, but reactivity was not restricted to protein surface epitopes. One monoclonal epitope was relatively surface accessible and in close proximity to an N-linked glycosylation site, while three others required additional thermal energy to expose the epitopes. The monoclonal antibodies demonstrated the capacity to differentiate progressive structural changes in IDS and could be used to characterize the severity of MPS type II in patients based on variable denatured microstates.
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Project description:The health state of an individual is closely linked to the glycosylation patterns of their blood plasma proteins. However, obtaining this information requires cost- and time-efficient analytical methods. We put forward infrared spectroscopy, which allows label-free analysis of protein glycosylation, but so far has only been applied to analyses of individual proteins. Although spectral information does not directly provide the molecular structure of the glycans, it is sensitive to changes therein and covers all types of glycosidic linkages. Combining single-step ion exchange chromatography with infrared spectroscopy, we developed a workflow that enables separation and analysis of major protein classes in blood plasma. Our results demonstrate that infrared spectroscopy can identify different patterns and global levels of glycosylation of intact plasma proteins. To showcase the strengths and limitations of the proposed approach, we compare the glycoforms of human and bovine alpha-1-acid glycoproteins, which exhibit highly variable global levels of glycosylation. To further independently evaluate our conclusions, the glycan moieties of human alpha-1-acid glycoprotein were further analyzed using established glycomics workflow. Importantly, the chromatographic separation of blood plasma improves the detection of aberrant glycoforms of a given protein, as compared to infrared spectroscopy of bulk plasma. The presented approach allows time-efficient comparison of glycosylation patterns of multiple plasma proteins, opening new avenues for biomedical probing.
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Project description:A heparin derivative that had been O/N-desulphated and re-N-acetylated was investigated by 13C n.m.r. spectroscopy and potentiometric titration. Three forms of uronic acid were observed, tentatively identified as beta-D-glucuronate, and two different forms of alpha-L-iduronate. A comparison of the n.m.r. spectra of heparin, an oligosaccharide (beta-D-glucuronate-2-acetamido-2-deoxy-alpha-D-glucose)n, and heparin that had been subjected to selective oxidation of beta-D-glucuronate, enabled the position of the anomeric carbon of the latter residue to be assigned [delta 102.9 (p.p.m.)]. Periodate oxidation of O/N-desulphated heparin destroyed in addition, approx. 40% of the alpha-L-iduronate content. The remainder of the alpha-L-iduronate residues displayed only one anomeric resonance, at delta 99.7 (p.p.m.). In another preparation, after sequential desulphation of heparin (N-desulphation, re-N-acetylation and O-desulphation) the anomeric resonance of the alpha-L-iduronate residue shifted downfield [from delta99.7 (p.p.m.) to delta 102.3]indicating a change in ring conformation. These data support the interpretation that the unsulphated alpha-L-iduronate residues may adopt two conformations. It was shown that the proportions of alpha-L-iduronate conformers are determined by the sequence of desulphation operations. Also minor components of heparin were assigned.
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