title: The solution structure of heparan sulfate differs from that of heparin: implications for function.
abstract: The highly sulfated polysaccharides heparin and heparan sulfate (HS) play key roles in the regulation of physiological and pathophysiological processes. Despite its importance, no molecular structures of free HS have been reported up to now. By combining analytical ultracentrifugation, small angle x-ray scattering, and constrained scattering modeling recently used for heparin, we have analyzed the solution structures for eight purified HS fragments degree of polymerization 6-18 (dp6-dp18) and dp24, corresponding to the predominantly unsulfated GlcA-GlcNAc domains of heparan sulfate. Unlike heparin, the sedimentation coefficient s(20,)(w) of HS dp6-dp24 showed a small rotor speed dependence, where similar s(20,)(w) values of 0.82-1.26 S (absorbance optics) and 1.05-1.34 S (interference optics) were determined. The corresponding x-ray scattering measurements of HS dp6-dp24 gave radius of gyration (R(G)) values from 1.03 to 2.82 nm, cross-sectional radius of gyration (R(XS)) values from 0.31 to 0.65 nm, and maximum lengths (L) from 3.0 to 10.0 nm. These data showed that HS has a longer and more bent structure than heparin. Constrained scattering modeling starting from 5000-8000 conformationally randomized HS structures gave best fit dp6-dp16 molecular structures that were longer and more bent than their equivalents in heparin. No fits were obtained for HS dp18 or dp24, indicating their higher flexibility. We conclude that HS displays an extended bent conformation that is significantly distinct from that for heparin. The difference is attributed to the different predominant monosaccharide sequence and reduced sulfation of HS, indicating that HS may interact differently with proteins compared with heparin.
authors.affiliation: Department of Structural and Molecular Biology, Division of Biosciences, Darwin Building, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Sanaullah
authors.initials: S
authors.lastname: Khan
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Rodriguez
authors.forename: Rima
authors.initials: R
authors.lastname: Patel
authors.forename: Jayesh
authors.initials: J
authors.lastname: Gor
authors.forename: Barbara
authors.initials: B
authors.lastname: Mulloy
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Perkins
mesh_terms: D002236:Carbohydrate Conformation; D006493:Heparin / Q000737:chemistry*; D006497:Heparan Sulfate / Q000737:chemistry*; D013329:Structure-Activity Relationship
chemical_list: D006493:Heparin; D006497:Heparan Sulfate