title: Thermodynamics of binding of D-galactose and deoxy derivatives thereof to the L-arabinose-binding protein.
abstract: We report the thermodynamics of binding of d-galactose and deoxy derivatives thereof to the arabinose binding protein (ABP). The "intrinsic" (solute-solute) free energy of binding DeltaG degrees (int) at 308 K for the 1-, 2-, 3-, and 6-hydroxyl groups of galactose is remarkably constant (approximately -30 kJ/mol), despite the fact that each hydroxyl group subtends different numbers of hydrogen bonds in the complex. The substantially unfavorable enthalpy of binding (approximately 30 kJ/mol) of 1-deoxygalactose, 2-deoxygalactose, and 3-deoxygalactose in comparison with galactose, cannot be readily accounted for by differences in solvation, suggesting that solute-solute hydrogen bonds are enthalpically significantly more favorable than solute-solvent hydrogen bonds. In contrast, the substantially higher affinity for 2-deoxygalactose in comparison with either 1-deoxygalactose or 3-deoxygalactose derives from differences in the solvation free energies of the free ligands.
authors.affiliation: Astbury Centre for Structural Molecular Biology, School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Antonio Hernandez
authors.initials: AH
authors.lastname: Daranas
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shimizu
authors.forename: Steve W
authors.initials: SW
authors.lastname: Homans
mesh_terms: D002151:Calorimetry / Q000379:methods; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D029968:Escherichia coli Proteins; D005643:Fucose / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D005690:Galactose / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011485:Protein Binding; D013816:Thermodynamics
chemical_list: C016242:AraF protein, E coli; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D005643:Fucose; D005690:Galactose