An NMR and Molecular Modeling Study of the Site-Specific Binding of Histamine by Heparin, Chemically Modified Heparin, and Heparin-Derived Oligosaccharides

• Published in: Biochemistry (Easton) 2000-04, Vol.39 (13), p.3542-3555
• Main Authors: Chuang, Wei-Lien, Christ, Marie Dvorak, Peng, Jie, Rabenstein, Dallas L
• Format: Article
• Language: English
• Subjects: Animals; Binding Sites; Carbohydrate Conformation; Carbohydrate Sequence; Cattle; Heparin - analogs & derivatives; Heparin - chemistry; Heparin - metabolism; Heparitin Sulfate - chemistry; Heparitin Sulfate - metabolism; Histamine - chemistry; Histamine - metabolism; Hydrogen-Ion Concentration; Iduronic Acid - chemistry; Iduronic Acid - metabolism; Models, Molecular; Molecular Sequence Data; Nuclear Magnetic Resonance, Biomolecular; Oligosaccharides - chemistry; Oligosaccharides - metabolism; Protons; Swine; Titrimetry
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi9926025

The diprotonated form of histamine binds site-specifically to heparin, a highly sulfated 1→4 linked repeating copolymer comprised predominantly of 2-O-sulfo-α-l-iduronic acid (the I ring) and 2-deoxy-2-sulfamido-6-O-sulfo-α-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 1H 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 1C4 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 α-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.