An NMR and molecular modelling study on the solution conformation of Heparan Sulphate: new insights into the relationship between structure and function

A deeper insight into the structural biology of HS is key to understanding its nearuniversal
functional role as a co-receptor for growth factors and morphogens. Due to the
extreme difficulty in preparing homogeneous HS oligosaccharides for structural and
functional studies, traditionally, oligosaccharides derived from the related molecule
heparin are used as HS structural models. In this study a number of authentic HS derived
hexasaccharides, in addition to heparin derived hexasaccharides, have been purified in
sufficient quantity to permit a detailed NMR and molecular modelling based analysis of
their three dimensional structure. The primary sequence of one HS derived
oligosaccharide has never previously been published. Studies on all oligosaccharides and
their chemically de-2-O-sulphated derivatives have revealed additional new insights into
the structural influence of sulphate groups. Consistent with previous studies, at the
monosaccharide level, sulphation was found to influence iduronate conformational
behaviour. However, with the data presented, a number of gaps in the literature have now
been filled, and it is now possible for the first time to predict the balance of iduronate
conformational equilibria within any HS monosaccharide sequence. Sulphation was also
found to influence the overall topology of the oligosaccharide chains themselves. In
particular, for the first time NMR data is presented to show that local deviations may
occur along the helical axis of each oligosaccharide when it is free in solution.
Polyacrylamide gel electrophoresis data and molecular dynamic modelling data are
presented to suggest that the rate at which local deviations occur may be influenced by
the sulphation pattern contained within a particular oligosaccharide. The functional
implications of these and other new structural insights are discussed, and in particular are
related to a library of HS derived decasaccharide structures previously tested for
biological activity