Micelle-assisted protein folding. Denatured rhodanese binding to cardiolipin-containing lauryl maltoside micelles results in slower refolding kinetics but greater enzyme reactivation

Abstract

Unfolded (inactive) rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) can be reactivated in the presence of detergents, e.g. lauryl maltoside (LM). Here, we report the reactivation of urea-unfolded rhodanese in the presence of mixed micelles containing LM and the anionic mitochondrial phospholipid, cardiolipin (CL). Reactivation times increased as the number of CL molecules/micelle was increased. A maximum of 94% of the activity was recovered at 2.2 CL/micelle. Only 71% of the activity was recovered in the absence of CL. The major zwitterionic mitochondrial phospholipid, phosphatidylcholine (PC), had no effect on the LM-assisted reactivation of rhodanese. Size exclusion chromatography showed that denatured, but not native, rhodanese apparently binds to micellar amounts of LM and CL/LM, but not to PC/LM micelles. The lifetime of the enzyme-micelle complex increased with the number of CL molecules/micelle. Furthermore, chromatographic fractions containing micelle-bound enzyme had no activity, while renatured rhodanese-containing fractions were active. These results suggest that transient complexes form between enzyme and both LM and CL/LM micelles, and that this complex formation may be necessary for reactivation. For CL/LM micelles, interactions may occur between the positively charged amino-terminal sequence of rhodanese and the negatively charged CL phosphate. Finally, this work shows that there are similarities between "micelle-assisted" and chaperonin-assisted rhodanese refolding.