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Biophys J, November 2002, p. 2812-2825, Vol. 83, No. 5

13C-1H NMR Relaxation and Fluorescence Anisotropy Decay Study of Tyrosine Dynamics in Motilin

Peter Damberg,* Jüri Jarvet,* Peter Allard,dagger Ülo Mets,Dagger Rudolf Rigler,Dagger and Astrid Gräslund*

 *Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, S-106 91 Stockholm, Sweden;  dagger Structural Biochemistry, Department of Biotechnology, Stockholm Center for Physics, Astronomy, and Biotechnology, The Royal Institute of Technology, S-106 91 Stockholm, Sweden; and  Dagger Department of Medical Biophysics, Karolinska Institute, S-171 77 Stockholm, Sweden

Tyrosine ring dynamics of the gastrointestinal hormone motilin was studied using two independent physical methods: fluorescence polarization anisotropy decay and NMR relaxation. Motilin, a 22-residue peptide, was selectively 13C labeled in the ring epsilon -carbons of the single tyrosine residue. To eliminate effects of differences in peptide concentration, the same motilin sample was used in both experiments. NMR relaxation rates of the tyrosine ring Cepsilon -Hepsilon vectors, measured at four magnetic field strengths (9.4, 11.7, 14.1, and 18.8 Tesla) were used to map the spectral density function. When the data were analyzed using dynamic models with the same number of components, the dynamic parameters from NMR and fluorescence are in excellent agreement. However, the estimated rotational correlation times depend on the choice of dynamic model. The correlation times estimated from the two-component model-free approach and the three-component models were significantly different (1.7 ns and 2.2 ns, respectively). Various earlier studies of protein dynamics by NMR and fluorescence were compared. The rotational correlation times estimated by NMR for samples with high protein concentration were on average 18% longer for folded monomeric proteins than the corresponding times estimated by fluorescence polarization anisotropy decay, after correction for differences in viscosity due to temperature and D2O/H2O ratio.

Biophys J, November 2002, p. 2812-2825, Vol. 83, No. 5
© 2002 by the Biophysical Society   0006-3495/02/11/2812/14  $2.00


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