Disassembly intermediates of RbsD protein remain oligomeric despite the loss of an intact secondary structure

Many proteins exist as homo-oligomers in living organisms wherein the change of oligomeric status apparently serves as an effective means for modulating their biological activities. We have previously reported that the homo-decameric RbsD from Escherichia coli undergoes stepwise disassembly and non-stepwise reassembly. Here the structural status of the urea-induced RbsD disassembly intermediates was examined, mainly using urea-containing polyacrylamide gel electrophoresis and chemical cross-linking. Such intermediates were found to remain oligomeric while losing their intact secondary structures. Such disassembly intermediates were able to effectively refold when the concentration of the urea denaturant was reduced to a lower level, or to refold/reassemble into the native decamers when urea was completely removed, as detected by non-denaturing polyacrylamide gel electrophoresis. These novel observations strongly suggest that the assembly of oligomeric proteins may occur before the completion of subunit folding.