Glycobiology Advance Access originally published online on June 18, 2007
Glycobiology 2007 17(9):983-993; doi:10.1093/glycob/cwm062
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Influence of substitution pattern and cation binding on conformation and activity in heparin derivatives
2 School of Biological Sciences, University of Liverpool, Liverpool L69 7ZB, UK
3 Ronzoni Institute for Chemical and Biochemical Research, Via G. Colombo 81, Milan 20133, Italy
4 CCLRC, Daresbury Laboratory, Warrington, Cheshire WA4 4AD, UK
1 To whom correspondence should be addressed: Tel: +44-151-795-4429; Fax: +44-151-795-4406; e-mail: eayates{at}liv.ac.uk
Received on April 25, 2007; revised on June 4, 2007; accepted on June 5, 2007
As model compounds for the biologically important heparan sulfate, eight systematically modified heparin derivatives were studied by synchrotron radiation circular dichroism (SRCD), which is sensitive to uronic acid confor- mation. Substitution pattern altered uronic acid conformation, even when structural changes were made in adjacent glucosamine residues (e.g. 6-O-desulfation) and did not involve a chromophore. SRCD spectra of these derivatives following conversion to the Na+, K+, Mg2+, Ca2+, Mn2+, Cu2+ and Fe3+ cation forms revealed that almost all substitution/cation combinations resulted in unique spectra, showing that each was structurally distinct. The detailed effects that binding Na+, K+, Mg2+ and Ca2+ ions had on a 2-de-O-sulfated derivative was also studied by NMR, revealing that subtle changes in conformation (by NOE) and flexibility (by T2 measurements) resulted. Conversion to the K+ and Cu2+ ion forms also drastically modified biological activity, from inactive to active, in a cell-based assay of fibroblast growth factor-receptor (FGF2/FGFR1c) signalling and this effect was not reproduced by free cations. These observations could explain the often-contradictory data concerning structure–activity relationships for these derivatives in the literature and, furthermore, argue strongly against the established trend of considering sequence as a complete structural definition. It also provides additional means of modifying the activity of these polysaccharides and suggests a possible additional level of control in biological systems. There are also obvious potential applications for these findings in the biotechnology sphere.
Key words: cations / fibroblast growth factor / heparin / heparan sulfate / synchrotron radiation circular dichroism
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