Multiphasic denaturation of the lambda repressor by urea and its implications for the repressor structure. |
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Authors: | U Banik R Saha N C Mandal B Bhattacharyya S Roy |
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Affiliation: | Department of Biophysics, Bose Institute, Calcutta, India. |
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Abstract: | Urea denaturation of the lambda repressor has been studied by fluorescence and circular dichroic spectroscopies. Three phases of denaturation could be detected which we have assigned to part of the C-terminal domain, N-terminal domain and subunit dissociation coupled with further denaturation of the rest of the C-terminal domain at increasing urea concentrations. Acrylamide quenching suggests that at least one of the three tryptophan residues of the lambda repressor is in a different environment and its emission maximum is considerably blue-shifted. The transition in low urea concentration (midpoint approximately 2 M) affects the environment of this tryptophan residue, which is located in the C-terminal domain. Removal of the hinge and the N-terminal domain shifts this transition towards even lower urea concentrations, indicating the presence of interaction between hinge on N-terminal and C-terminal domains in the intact repressor. |
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