title: Role of CH/pi interactions in substrate binding by Escherichia coli beta-galactosidase.
abstract: Interactions between carbohydrates and aromatic amino-acid residues are often observed in structures of carbohydrate-protein complexes. They are characterized by an orientation of the pyranose or furanose ring parallel with the aromatic ring of amino-acid residues. An important role in the formation of these complexes is supposed to be played by CH/pi interactions. This paper presents an ab initio quantum chemistry study of CH/pi interactions between beta-galactosidase from E. coli and its substrates and products. The energy stabilizing the interaction between Trp999 residue and substrate bound in the shallow binding mode was calculated at the MP2/6-31+G(d) level as 5.2kcalmol(-1) for the glucose moiety of allolactose, 2.4kcalmol(-1) for the galactose moiety of allolactose and 5.0kcalmol(-1) for the glucose moiety of lactose. The energy stabilizing the interaction between Trp568 residue and galactose in the deep binding mode was calculated as 2.7kcalmol(-1). Interaction energies at the HF/6-31+G(d) and B3LYP/6-31+G(d) levels were small or repulsive; therefore, highly correlated ab initio methods were necessary to study these interactions. These unexpectedly strong interactions give a rationale for allolactose formation and illustrate the role of the Trp999 residue. In addition, this illustrates the importance of CH/pi interactions for the function of carbohydrate-binding proteins and carbohydrate-processing enzymes.
authors.affiliation: Department of Biochemistry and Microbiology, Institute of Chemical Technology in Prague, Technická 3, Praha 6, 166 28, Czech Republic.
authors.forename: Vojtech
authors.initials: V
authors.lastname: Spiwok
authors.forename: Petra
authors.initials: P
authors.lastname: Lipovová
authors.forename: Tereza
authors.initials: T
authors.lastname: Skálová
authors.forename: Eva
authors.initials: E
authors.lastname: Buchtelová
authors.forename: Jindrich
authors.initials: J
authors.lastname: Hasek
authors.forename: Blanka
authors.initials: B
authors.lastname: Králová
mesh_terms: D001665:Binding Sites; D002151:Calorimetry; D002244:Carbon; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000378:metabolism; D006601:Hexoses / Q000737:chemistry / Q000378:metabolism; D006859:Hydrogen; D013379:Substrate Specificity; D013816:Thermodynamics; D001616:beta-Galactosidase / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D006601:Hexoses; D002244:Carbon; D006859:Hydrogen; D001616:beta-Galactosidase