title: Anomalous binding profile of phenylboronic acid with N-acetylneuraminic acid (Neu5Ac) in aqueous solution with varying pH.
abstract: Borates are known to interact with carbohydrate moieties expressed on the surface of biological membranes of a variety of cells, viruses, bacteria, and fungi. This study revealed the anomalous binding profile of borate in aqueous solution with N-acetylneuraminic acid (Neu5Ac, sialic acid) as a potential receptor site on the surfaces of biological membranes using (11)B, (1)H, (13)C, and (15)N nuclear magnetic resonance spectroscopies. 3-(Propionamido)phenylboronic acid (PAPBA) was chosen as the model borate compound. The equilibrium constant (K) for Neu5Ac binding to PAPBA was compared with those for glucose, mannose, and galactose, which are the major carbohydrate constituents of glycoproteins and glycolipids expressed on biological membranes. In the Neu5Ac/PAPBA system, the unusual pH dependency of the K values, a decrease in K with increasing pH, was observed, suggesting the formation of a trigonal-formed complex stabilized by the coordination of an amide group of Neu5Ac at the C-5 position to the boron atom, forming intramolecular B-N or B-O bonding. Furthermore, the anomalously high complexing ability at physiological pH 7.4 was confirmed for this system, with the K value 37.6 which is approximately 7 times higher than that for glucose. This exceptionally high value of K at physiological pH, compared to those of other sugars, strongly suggests that the boronic acid selectively recognizes the Neu5Ac residues of the glycosylated components including glycoproteins and gangliosides existing on the surface of the biological membranes.
authors.affiliation: Department of Materials Science and Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Otsuka
authors.forename: Eiichiro
authors.initials: E
authors.lastname: Uchimura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Koshino
authors.forename: Teruo
authors.initials: T
authors.lastname: Okano
authors.forename: Kazunori
authors.initials: K
authors.lastname: Kataoka
mesh_terms: D001897:Boronic Acids / Q000737:chemistry*; D005690:Galactose / Q000737:chemistry; D005947:Glucose / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008358:Mannose / Q000737:chemistry; D008968:Molecular Conformation; D019158:N-Acetylneuraminic Acid / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D012996:Solutions; D014867:Water / Q000737:chemistry
chemical_list: D001897:Boronic Acids; D012996:Solutions; D014867:Water; C096881:3-propionamidophenylboronic acid; D019158:N-Acetylneuraminic Acid; D005947:Glucose; D008358:Mannose; D005690:Galactose