Multivalent presentation of carbohydrates by 3₁₄-helical peptide templates: synthesis, conformational analysis using CD spectroscopy and saccharide recognition

Abstract

A well defined 314-helical tetravalent β-galactopeptide site-specific functionalised template (SSFT) 1 was prepared containing d-galactose units, with free anomeric carbons as the aldehyde tags, and was explored via ligation with different aminoxy sugars (α-/β-d-glucose, α/β-d-galactose, α-d-mannose and β-d-lactose) to get 314-helical carbohydrate-functionalised multivalent glycoconjugates 2-7. Preliminary recognition studies of tetramannosyl glycoconjugate 4 with a specific lectin (concanavalin A) using fluorescence anisotropy showed an increase in binding affinity and the multivalency effect was found to be increased by 6.5 times per glycan.

Supramolecular Recognition and Selective Protein Uptake by Peptide Hybrids

“…Incubation of the fluorescently‐labeled glycopeptides with increasing amounts of native ConA resulted in a gradual increase of the anisotropy, which indicates the formation of a higher molecular weight complex with the protein host (Figure A) . Initial control experiments with fluorescently labeled methyl α‐ d ‐mannopyranoside and fitting to a 1:1 binding model allowed the estimation of a K d of 137±29 μ m , which is consistent with reported values ( K d ≈100 μ m ) . The peptide Tm P (Man) 2 , which contains two orthogonal mannoses, showed the maximum net anisotropy value and the best equilibrium dissociation constant ( K d =14±1 μ m ), which was about one order of magnitude higher than that of the mannoside control (Figure A).…”

“…For this purpose, ConA was initially saturated with af luorescently labeled a-dmannopyranoside.T he resulting complexw as titrated with the competitor that displaced the ligand from its binding site (Figure 2B). [31] As expected, the peptide with the two orthogonal mannoses wast he best competitor.T his peptide was able to remove practically all of the labeled mannoside at the lowest concentration( IC 50 = 98 AE 6 mm). The control peptide with only one mannosew as less efficient and required more than double the concentration to remove only part of the fluorescent mannopyranoside (IC 50 = 228 AE 21 mm).…”

“…For this purpose, ConA was initially saturated with a fluorescently labeled α‐ d ‐mannopyranoside. The resulting complex was titrated with the competitor that displaced the ligand from its binding site (Figure B) . As expected, the peptide with the two orthogonal mannoses was the best competitor.…”

“…[54] Initial control experiments with fluorescently labeled methyl a-d-mannopyranoside and fitting to a1 :1 binding model allowed the estimation of a K d of 137 AE 29 mm,w hich is consistentw ithr eported values (K d % 100 mm). [31,53] The peptide TmP(Man) 2 ,w hich containst wo orthogonal mannoses, showed the maximum net anisotropy value and the best equilibrium dissociation constant( K d = 14 AE 1 mm), which was about one order of magnitude highert han that of the mannoside control ( Figure 2A). The role of the mannosef or protein binding was confirmed by removal of the glycans.…”

“…[27] Reports on peptidef olding for improvedg lycan presentation and lectin binding can be found scattered throughout the literature. [28][29][30][31] Furthermore, lectins are commonlyo verexpressed during tissue inflammationa nd cellular metastasis. [27,32] As aconsequence, the delivery of exogenous lectins and their conjugates has been explored in the context of cell targeting and cancert herapy.…”