title: A study of energetics of cooperative interaction using a mutant lambda-repressor.
abstract: A lambda-repressor mutant, S228N, which is defective in tetramer formation in the free state but retains full cooperativity, was studied in detail. Isolated single operator-bound S228N repressor shows association properties similar to those of the wild-type repressor. Fluorescence anisotropy studies with dansyl chloride-labeled repressor show a dimer-monomer dissociation constant of around 10(-5) M. The structure of the mutant repressor was studied by circular dichroism, acrylamide quenching and sulfhydryl reactivity at protein concentrations of < or =10(-6) M, where it is predominantly monomeric. The results suggest no significant perturbations in the structure of the S228N mutant repressor from that of the wild-type repressor. Urea denaturation studies also indicate no significant change in the stability of the repressor. The results were used to calculate energetics of loop formation in the cooperative binding process.
authors.affiliation: Department of Biochemistry and Department of Biophysics, Bose Institute, Acharya J. C. Bose Birth Centenary Building, P 1/12 C.I.T Scheme VII M, Calcutta 700 054, India.
authors.forename: N K
authors.initials: NK
authors.lastname: Jana
authors.forename: S
authors.initials: S
authors.lastname: Deb
authors.forename: B
authors.initials: B
authors.lastname: Bhattacharyya
authors.forename: N C
authors.initials: NC
authors.lastname: Mandal
authors.forename: S
authors.initials: S
authors.lastname: Roy
mesh_terms: D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D019281:Dimerization; D004735:Energy Transfer; D005453:Fluorescence; D009154:Mutation; D011487:Protein Conformation; D011489:Protein Denaturation; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D014508:Urea / Q000737:chemistry; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins; D014508:Urea