Stabilization of partially folded states of cytochrome c in aqueous surfactant: effects of ionic and hydrophobic interactions.
The interaction of submicellar concentrations of sodium dodecyl sulfate (SDS) with horse heart cytochrome c has been found to stabilize two spectroscopically distinct partially folded intermediates at pH 7. The first intermediate is formed by the interaction of SDS with native cytochrome c, and this intermediate retains the majority of the secondary structure while the tertiary structure of the protein is lost. The unfolding of this intermediate with urea leads to the formation of a second intermediate, which is also formed on refolding of the unfolded protein (unfolded by urea) by SDS. The second intermediate retains about 50% of the native secondary structure with no tertiary structure of the protein. The second intermediate was found to be absent at low pH. While induction of helical structure of a protein by SDS in the native condition has been reported earlier, this is possibly the first report of the refolding of a protein in a strongly denaturing condition (in the presence of 10 M urea). The relative contributions of the hydrophobic and the electrostatic interactions of the surfactants with cytochrome c have been determined from the formation of the molten globule species from the acid-induced unfolded protein in the presence of SDS or lauryl maltoside.
Chattopadhyay
Krishnananda
K
Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India.
Mazumdar
Shyamalava
S
D000818:Animals; D002942:Circular Dichroism; D045304:Cytochromes c / Q000737:chemistry*; D004795:Enzyme Stability; D006736:Horses; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007477:Ions; D007700:Kinetics; D011489:Protein Denaturation; D017510:Protein Folding; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D055672:Static Electricity; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics; D014508:Urea / Q000737:chemistry; D014867:Water / Q000737:chemistry
D007477:Ions; D013501:Surface-Active Agents; D014867:Water; D012967:Sodium Dodecyl Sulfate; D014508:Urea; D045304:Cytochromes c