Folding and stability of a fibronectin type III domain of human tenascin

The folding of an isolated fibronectin type III domain of human tenascin, a large extra-cellular matrix protein, has been characterised. The isolated module, which has no disulphide bonds, can be reversibly unfolded by chemical denaturant and temperature. Equilibrium unfolding, measured using a number of different probes, fits to a two-state transition, with consistent measures of DeltaGH2OD-N. Folding and refolding rate constants have been determined over a range of denaturant concentrations. The refolding kinetics are bi-phasic, and in the transition region the slow phase dominates refolding kinetics. Outside the transition region the folding of the fast-folding species fits to a two-state model. There is no evidence for significant accumulation of partially folded intermediates.