Reversible structural changes in a hydrophobic protein, elastin, as indicated by fluorescence probe analysis

Fluorescent probe analysis of purified elastin using 1‐anilinonaphthalene‐8‐sulfonate has been used to investigate reversible structural changes that accompany stretching of this rubberlike protein. There is a specific binding of 1‐anilinonaphthalene‐8‐sulfonate to elastin with a single dye molecule attached per 74,000 molecular‐weight protein subunit. When labeled elastin is stretched, the intensity of the 1‐anilinonaphthalene‐8‐sulfonate fluorescence decreases reversibly, and this decrease appears to be linked to an increase in the environmental polarity in the immediate vicinity of the bound dye molecule. The results of experiments carried out in H 2 O and D 2 O indicate that this polarity change is due to an increase in the exposure of the 1‐anilinonaphthalene‐8‐sulfonate to water as the hydrophobic interior of the protein subunit is unfolded during stretching. The data are consistent with the proposal that the elastin network is a two‐phase system of hydrophobic protein globules surrounded by free solvent spaces.