The backbone dynamics of a partially folded, N-terminal fragment of E. coli thioredoxin were investigated using nuclear magnetic resonance spectroscopy (NMR). Relaxation data were collected at three temperatures and analyzed using reduced spectral density mapping. As temperature was increased, the values for the viscosity normalized J(0) and for J(ω_H) increased, while J(ω_N) decreased. The global trend observed for the viscosity normalized J(0) was consistent with an increase in the hydrodynamic volume of the fragment and suggested the presence of correlated rotational motion in the absence of long range interactions. In addition, the residue specific variation observed for the viscosity normalized J(0) suggested contributions to J(ω) from a range of correlation times that are close to the global correlation time.

Key words: Spectral density, Backbone dynamics, Hydrodynamic volume, Thioredoxin.