Renaturation of Myoglobin Denatured by Sodium Dodecyl Sulfate by Removal of Dodecyl Sulfate Ions Bound to the Protein Using Sodium Cholate

The secondary and tertiary structures of myoglobin were disrupted by sodium dodecyl sulfate (SDS) but were hardly affected by the bile salt, sodium cholate (NaCho). This disruption was induced by the binding of dodecyl sulfate (DS) ions to the protein. In this study, the removal of DS ions bound to the protein was attempted using NaCho. The extent of removal of DS ions was estimated by the restoration of the secondary and tertiary structures of the protein disrupted by SDS. The secondary structural change was followed by monitoring mean residue ellipticity at 222 nm, [01222, which was frequently used as a measure of alpha-helical content. The tertiary structural change was followed by examining the Soret band absorbance of the protein. Evidently, the magnitude of [01222 of myoglobin in the SDS solution initially decreased and then increased back to almost its original value as the NaCho concentration increased. The initial decrease in [01222 indicated the cooperation of NaCho and SDS in disrupting the secondary structure at low concentrations of both surfactants. This cooperation was also observed in the tertiary structural change as a shift of the Soret band maximum wavelength, lambda max, and a decrease in the molar absorption coefficient, epsilon max, at lambda max. Above a certain NaCho concentration, the position of lambda max and the magnitude of epsilon max were also restored to their original states. The secondary and tertiary structures were simultaneously restored by adding NaCho. These recoveries were attributed to removal of the DS ions bound to the protein. This removal might be due to the ability of cholate anions to strip DS ions bound to the protein. The stripped DS ions are more likely to form SDS-NaCho mixed micelles in bulk than SDS-NaCho mixed aggregates on the protein.

Automated summary

In this study, the removal of dodecyl sulfate (DS) ions bound to myoglobin protein was attempted using sodium cholate (NaCho). The restoration of the secondary and tertiary structures of myoglobin disrupted by sodium dodecyl sulfate (SDS) was achieved by the removal of DS ions. The cooperative action of NaCho and SDS was observed in disrupting the secondary and tertiary structures at low concentrations of both surfactants.