Hydrogendeuterium exchange studies of the rat thyroid transcription factor 1 homeodomain
Authors: Esposito G.; Fogolari F.; Damante G.; Formisano S.; Tell G.; Leonardi A.; Lauro R.D.; Viglino P.
Source: Journal of Biomolecular NMR, Volume 9, Number 4, June 1997 , pp. 397-407(11)
The ^1H NMR solution structure of the rat thyroid transcription factor 1 homeodomain (TTF-1 HD) showed that the molecule folds like classical homeodomains. The C-terminal extension of helix III (fragment 5159) appeared to adopt a helical geometry, albeit not as rigid as the preceding portion, but the hydrogendeuterium exchange of backbone amides and the NOE data provided evidence of a discontinuity between the two moieties of helix III at the highly conserved fragment Asn^51His^52Arg^53. Analysis of quantitative measurements of isotope exchange rates allows one to recognize the general occurrence, in that region of HD motifs, of opposite effects to helix III stability. Asparagine, histidine and arginine residues occur most frequently at the beginning and end of protein helices. In TTF-1 HD a local fluctuation is observed in the fragment 5153 which either kinks or tightens the -helix. A search through the protein structure database reveals that the three most common variants of HD fragments 5153 are often involved in helices and, frequently, in helix initiation or termination. For homeodomains in general, the nature of the fragment 5153 may be related to the conformational dynamics of their DNA-recognition helix (helix III). Besides the specific results on fragment 5153, the complete isotope exchange analysis of TTF-1 HD data shows that the partially solvent-exposed recognition helix is stabilized by hydrophobic interactions, like most of the structured regions of the molecule. Hydrophobic stabilization of the contacting regions meets the requirements of a DNA-interaction mechanism which, as shown with other DNA-protein complexes, should entail negative heat capacity variations due to changes in solvent exposure of the nonpolar protein surface.
Document Type: Regular paper
Publication date: 1997-06-01