Physical properties of the glycoprotein of vesicular stomatitis virus measured by intrinsic fluorescence and aggregation.

We have studied the denaturation and renaturation of the purified glycoprotein (G) of vesicular stomatitis virus by using intrinsic fluorescence spectroscopy and an aggregation assay. Our studies were carried out with G containing two complex oligosaccharide chains, with the asialo form of the protein, and for some experiments with G containing altered oligosaccharide structures. Fluorescence quenching using acrylamide showed no differences between the native and denatured states of G due to sialic acid content. Denaturation by guanidinium chloride (GdmCl) at 25 degrees C was reversible for the major transition region. The data analyzed by a two-state denaturation model gave a free energy of unfolding in the absence of denaturant of approximately 1.4 kcal/mol. For renaturation, two types of dialysis protocols were employed. The first (direct dialysis) involved dialysis against standard buffer [140 mM NaCl, 10 mM sodium phosphate, 1 mM disodium ethylenediaminetetraacetate, and 0.2% (w/v) poly(oxyethylene) 10-tridecyl ether, pH 7.4]. Recovery of the native emission maximum did not occur for any of the G proteins by using this procedure. The second (annealing dialysis) involved slow removal of GdmCl against decreasing concentrations of GdmCl in standard buffer over a period of 2-3 days. Only in this case was recovery of the native emission maximum and fluorescence intensity obtained. For those G proteins in which the oligosaccharide chains were decreased in size, this protocol led to extensive aggregation.