NMR studies on binding sites and aggregation–disassociation of fluorinated surfactant sodium perfluorooctanoate on protein ubiquitin

The fluorinated surfactant sodium perfluorooctanoate (SPFO) could bind onto ubiquitin (UBQ) and induce the unfolding of UBQ. By using 15N-edited heteronuclear single-quantum coherence (HSQC) NMR and 19F NMR to monitor 15N-labeled UBQ and SPFO, respectively, the binding sites and the aggregation process of SPFO on UBQ at various SPFO concentrations were observed. A detailed process from specific binding to cooperative binding of SPFO on UBQ, and a detailed structure change of UBQ upon the increase of SPFO concentration were obtained. The refolding of UBQ in UBQ–SPFO complex was carried out by adding cationic surfactant. It was shown that added cationic surfactants formed mixed micelles with SPFO and resulted in the dissociation of the UBQ–SPFO complex, and consequently, most ubiquitin could be refolded to its native state.