title: An NMR and molecular modeling study of the site-specific binding of histamine by heparin, chemically modified heparin, and heparin-derived oligosaccharides.
abstract: The diprotonated form of histamine binds site-specifically to heparin, a highly sulfated 1-->4 linked repeating copolymer comprised predominantly of 2-O-sulfo-alpha-L-iduronic acid (the I ring) and 2-deoxy-2-sulfamido-6-O-sulfo-alpha-D-glucopyranosyl (the A ring). The binding is mediated by electrostatic interactions. The structural features of histamine and heparin, which are required for the site-specific binding, have been identified from the results of (1)H NMR studies of the binding of histamine by six heparin-derived oligosaccharides and four chemically modified heparins and molecular modeling studies. The results indicate that the imidazolium ring of diprotonated histamine is critical for directing site-specific binding, while the ammonium group increases the binding affinity. The imidazolium ring binds within a cleft, with the A ring of an IAI triad at the top of the cleft, and the I rings forming the two sides. The H3 proton of the A ring is in the shielding cone of the imidazolium ring. The carboxylate group of the I-ring at the reducing end of the IAI triad and possibly the sulfamido group of the A-ring are essential for site-specific binding, whereas the 2-O-sulfate group of the I ring and the 6-O-sulfate group of the A ring are not. The results indicate that histamine binds to the IAI triad with the I rings in the (1)C(4) conformation. Also, the configuration of the carboxylate group is critical, as indicated by the absence of site-specific binding of histamine by the related IAG sequence, where G is alpha-D-glucuronic acid. The molecular modeling results indicate that the N1H and N3H protons of the imidazolium ring of site-specifically bound histamine are hydrogen bonded to the carboxylates of the I rings at the nonreducing and reducing ends of the IAI trisaccharide sequence.
authors.affiliation: Department of Chemistry, University of California Riverside, California 92521, USA.
authors.forename: W L
authors.initials: WL
authors.lastname: Chuang
authors.forename: M D
authors.initials: MD
authors.lastname: Christ
authors.forename: J
authors.initials: J
authors.lastname: Peng
authors.forename: D L
authors.initials: DL
authors.lastname: Rabenstein
mesh_terms: D000818:Animals; D001665:Binding Sites; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002417:Cattle; D006493:Heparin / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism; D006497:Heparan Sulfate / Q000737:chemistry / Q000378:metabolism; D006632:Histamine / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007067:Iduronic Acid / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009844:Oligosaccharides / Q000737:chemistry* / Q000378:metabolism; D011522:Protons; D013552:Swine; D017186:Titrimetry
chemical_list: D006493:Heparin; D006497:Heparan Sulfate; D006632:Histamine; D007067:Iduronic Acid; D009844:Oligosaccharides; D011522:Protons