Trehalose-induced changes of the ethidium hydration shell detected by time-resolved fluorescence

Using high-performance liquid chromatography to measure the effects of protein-stabilizing cosolvents on a model protein and fluorescent probes

The effect of cosolvents on the fluorescence of solutes was measured manually and in an automated high-performance liquid chromatography (HPLC) system that eliminates fluorescent contaminants on-line. The HPLC system was used to show that the effect of cosolvents on the fluorescence spectrum of heated chymotrypsin (a measure of unfolding) correlates with the effect of the solutes on the heat stabilization of catalytic activity; r2=0.73 with 12 example cosolvents. Changes in the fluorescence of model probes showed that known counteracting solutes slightly decrease the polarity of the solvent. Different cosolvents affect the proton transfer indicator, 2-naphthol (a model for tyrosinyl residues) differently, polyhydric alcohols enhance the protonated naphthol emission whereas zwitterionic solutes enhance naphthoxide fluorescence. The results with the automated system are consistent with the known stabilizing effects of the cosolvents and validate it as a tool to explore the development of novel cosolvents and their effects on multiple biological systems.

Evidence of discrete substates and unfolding pathways in green fluorescent protein

We present evidence of conformational substates of a green fluorescent protein mutant, GFPmut2, and of their relationship with the protein behavior during chemical unfolding. The fluorescence of single molecules, excited by two infrared photons from a pulsed laser, was detected in two separate channels that simultaneously collected the blue or the green emission from the protein chromophore chemical states (anionic or neutral, respectively). Time recording of the fluorescence signals from molecules in the native state shows that the chromophore, an intrinsic probe sensitive to conformational changes, switches between the two states with average rates that are found to assume distinct values, thereby suggesting a multiplicity of protein substates. Furthermore, under denaturing conditions, the chromophore switching rate displays different and reproducible time evolutions that are characterized by discrete unfolding times. The correlation that is found between native molecules' switching rate values and unfolding times appears as direct evidence that GFPmut2 can unfold only along distinct paths that are determined by the initial folded substate of the protein.