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Detection of secondary structure in glycosaminoglycans via the H n.m.r. signal of the acetamido NH group.

ABSTRACT: Two simple methods for dissolving salts of acid glycosaminoglycans with inorganic cations (e.g. Li+ and Na+) in dry dimethyl sulphoxide are described. Complete n.m.r. spectra of, e.g., Na+ and Li+ salts of chondroitin sulphate and keratan sulphate were obtained on these solutions. In [2H6]dimethyl sulphoxide the NH resonance of 2-acetamido-2-deoxy hexosides is in the range 7.2-8.0 delta, but is downfield (8.3-9.3 delta) when the NH is H-bonded to -CO2-. Heparan sulphate shows two NH resonances, of which one (at 8.3 delta) is probably indicative of H-bonding. Space-filling models show that a very close approach of NH to -CO2- across the alpha-glucosaminidic bond is possible, and a solution configuration for heparan sulphate is proposed. The n.m.r. results are entirely compatible with interpretations of periodate-oxidation kinetics, based on H-bonded secondary structures present in hyaluronate and chondroitin sulphates, but not in dermatan (or keratan) sulphate.

SUBMITTER: Scott JE

PROVIDER: S-EPMC1153834 | biostudies-other | 1982 Oct

REPOSITORIES: biostudies-other

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Project description:Fibrillation of supramolecular building blocks represents an important model system for complex proteins and peptides, such as amyloidogenic proteins, displaying aggregation and subsequent collapse of their biological functions. In this work, we synthesized narrow-dispersed, end group-telechelic, oligomeric-(l-lysine(carboxybenzyl (Z)/trifluoroacetyl (TFA))) n s (n = 3-33) as a model system for studying assembly and secondary structure formation, prepared via ring opening polymerization (ROP) of N-carboxyanhydrides (NCA). Our primary goal was to understand the influence of amino acid chain length and end group-modification on the secondary structure and fibrillation of the oligo-Z/TFA-protected lysines. Synthesis was accomplished by initiation of ROP with 11-amino-undecene, followed by complete chain end functionalization reactions of the N-terminus by 10-undecenoyl-chloride. The so obtained oligomeric-(l-lysine(Z/TFA)) n s were fractionated according to their number of repeating units (n) with preparative GPC using DMF as the eluent. As proven by MALDI-ToF MS, 1H-NMR-spectroscopy and analytical GPC, they were separated into fractions with low polydispersity (Đ) values, ranging from 1.02-1.08. Secondary structural investigations of these narrowly-dispersed oligomeric-(l-lysine(Z/TFA)) n s (n = 33 ± 6, n = 18 ± 6, n = 12 ± 4, n = 5 ± 2) were accomplished by CD spectroscopy in TFE and HFIP, indicating that TFE was able to induce/stabilize the formation of α-helicity. Fibril formation of oligomeric-(l-lysine(Z/TFA)) n s with shorter chain lengths (n = 7 and n = 3) were chosen to investigate the effect of the number of repeating units' role on the self-assembly of the oligomers in TFE. TEM images of these selected fractions, f19 with n = 7 and f28 with n = 3, showed that fibrillization occured and the formation of a dense fibrillar mesh was observed when the amino acid chain length is equal to 7. Therefore, the influences of the number of repeating units (n), end-group functionalities (mono- or bis-functional) and the choice of solvents (TFE or HFIP) on the propensity to form helical structure allowed us to calibrate their secondary structure.

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Detection of secondary structure in glycosaminoglycans via the H n.m.r. signal of the acetamido NH group.

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