Abstract:
:We have studied the time-resolved fluorescence of three engineered Tet repressor (TetR) mutants bearing a single Trp residue at positions 162, 163, and 165 in the C-terminal part of the loop joining helices 8 and 9. Detailed analysis indicates that, at 20 degrees, the fluorescence decay of each Trp can be described as the sum of three exponential components with lifetimes in the 1-, 3-, and 6-ns range. Emission wavelength and temperature dependence studies are consistent with a model in which these components are due to the existence of three classes of Trp residues non-interconverting on the nanosecond timescale. Within the framework of the rotamer model, the weak temperature dependence of the lifetimes strongly suggests that the secondary structure of the loop, at least in the 162-165 range, is not altered with temperature. The equilibrium between the rotamers is characterized by an enthalpy-entropy compensation effect which strongly suggests the involvement of background structural regions of TetR in the thermodynamics of the process. The very high deltaH degrees and TdeltaS degrees observed (up to 18 kcal/ mol) should reflect the temperature-dependent conformational change of a large part of the protein which would alter the rotamer distribution of the Trp residues. Taken together, our results are consistent with the existence of (at least) two conformations of the loop and suggest a model for loop motion.
journal_name
Arch Biochem Biophysjournal_title
Archives of biochemistry and biophysicsauthors
Alberti P,Bombarda E,Kintrup M,Hillen W,Lami H,Piémont E,Doglia SM,Chabbert Mdoi
10.1006/abbi.1997.0290subject
Has Abstractpub_date
1997-10-15 00:00:00pages
230-40issue
2eissn
0003-9861issn
1096-0384pii
S0003-9861(97)90290-3journal_volume
346pub_type
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journal_title:Archives of biochemistry and biophysics
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journal_title:Archives of biochemistry and biophysics
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pub_type: 杂志文章
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pub_type: 杂志文章
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pub_type: 杂志文章
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