title: Ligand specificity and ligand-induced conformational change in gal repressor.
abstract: Gal repressor (GalR) binds D-galactose, which is responsible for lifting of repression of the gal operon. Proton T1 measurements of alpha- and beta-anomers of galactose as a function of gal repressor show preferential binding of the beta-anomer. The beta-anomer was isolated by high-performance liquid chromatography and was shown to bind tightly to GalR. Calorimetry was used to determine enthalpy changes at several temperatures. Heat capacity change was found to be positive, indicating that a significant amount of hydrophobic surface area was exposed upon galactose binding. Bis-ANS binding to GalR is significantly enhanced in the presence of a saturating amount of galactose, indicating additional exposure of hydrophobic surfaces. We propose that the galactose-induced conformational change involves the opening of the two subdomains, which may disrupt protein-protein interactions responsible for repression.
authors.affiliation: Department of Biophysics, Bose Institute, P-1/12 C.I.T. Scheme VII M, Calcutta, India.
authors.forename: Sumana
authors.initials: S
authors.lastname: Chatterjee
authors.forename: Kajari
authors.initials: K
authors.lastname: Ghosh
authors.forename: Amlanjyoti
authors.initials: A
authors.lastname: Dhar
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Roy
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D002151:Calorimetry; D002851:Chromatography, High Pressure Liquid; D029968:Escherichia coli Proteins; D005690:Galactose / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D057927:Hydrophobic and Hydrophilic Interactions; D007536:Isomerism; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D009876:Operon / Q000235:genetics; D011485:Protein Binding; D011487:Protein Conformation; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013379:Substrate Specificity; D013816:Thermodynamics; D017186:Titrimetry
chemical_list: D029968:Escherichia coli Proteins; C050993:Galactose repressor proteins; D008024:Ligands; D012097:Repressor Proteins; D005690:Galactose