title: Helix mobility and recognition function of the rat thyroid transcription factor 1 homeodomain - hints from 15N-NMR relaxation studies.
abstract: The backbone dynamics of the (15)N-labeled homeodomain of the rat thyroid transcription factor 1 has been studied by 2D NMR spectroscopy. Longitudinal (R(1)) and transverse (R(2)) (15)N relaxation rate constants and steady-state {(1)H}-(15)N NOEs were measured at 11.7 T. These data were analyzed by both the model-free formalism and the reduced spectral density mapping (RSDM) approaches. The global rotational correlation time, tau(m), of the thyroid transcription factor 1 homeodomain in aqueous solution at 286 K was found to be 10.51 +/- 0.05 ns by model-free formalism and 9.85 +/- 1.79 ns by RSDM calculation. The homogeneity of the values of the overall correlation time calculated from the individual (R(2)/R(1)) ratios suggested a good degree of isotropy of the global molecular motion, consistent with the similar global tau(m) results obtained with the two different methods. Tyr25 was found to undergo slow conformational exchange by both methods, whereas this contribution was identified also for Lys21, Gln22, Ile38 and His52 only by RSDM. With both methods, the C-terminal fragment of helix III was found to be more flexible than the preceding N-terminal portion, with slightly different limits between rigid and mobile moieties. Additionally, Arg53 appeared to be characterized by an intermediate motional freedom between the very flexible N-terminal and C-terminal residues and the structured core of the molecule, suggesting the occurrence of a hinge point. Finally, slow-time-scale motions observed at the end of helix I, at the end of helix II and within helix III appear to be consistent with typical fraying transitions at helical C-termini.
authors.affiliation: Dipartimento di Scienze e Tecnologie Biomediche, Università di Udine, Italy.
authors.forename: Devrim
authors.initials: D
authors.lastname: Gümral
authors.forename: Luana
authors.initials: L
authors.lastname: Nadalin
authors.forename: Alessandra
authors.initials: A
authors.lastname: Corazza
authors.forename: Federico
authors.initials: F
authors.lastname: Fogolari
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Damante
authors.forename: Paolo
authors.initials: P
authors.lastname: Viglino
authors.forename: Gennaro
authors.initials: G
authors.lastname: Esposito
mesh_terms: D000818:Animals; D003198:Computer Simulation; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008958:Models, Molecular; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D051381:Rats; D013816:Thermodynamics; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*
chemical_list: C000614416:Nkx2-1 protein, rat; D009687:Nuclear Proteins; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors