SDS Induced Refolding of Pre-molten Globule State of Cryptolepain: Differences in Chemical and Temperature-Induced Equilibrium Unfolding of the Protein in SDS-Induced State

Interaction of sodium dodecyl sulfate (SDS) with a globular protein cryptolepain to induce stabilization of the pre-molten globule state of the protein under acidic condition was studied. At pH 2.0, cryptolepain is in partially unfolded state with native like secondary structure, exposed hydrophobic surfaces without any rigid tertiary structure. Unfolding of cryptolepain in the pre-molten globule state (state at pH 2.0) is co-operative suggesting that the protein unfolds as a single entity. Addition of SDS below its critical micelle concentration of 2.0 mM at acidic pH drives the protein to a non-native state similar to molten globule state seen with other proteins. Temperature induced unfolding of such SDS-induced state of the cryptolepain is biphasic suggesting that the molecular structure of the protein is constituted of two structural entities which are stabilized differentially in the presence of SDS and unfold sequentially. Whereas the chemical induced unfolding of SDS-induced state of cryptolepain is co-operative with higher transition midpoints indicating that the protein is stabilized as a whole. Unfolding of SDS-induced state of cryptolepain is very similar to the unfolding of the cryptolepain at very low pH (0.5), where the protein exists in molten globule state. Thus, SDS interactions result in the refolding of the acid unfolded state of the protein and drive the protein into a non-native state similar to the molten-globule state seen at very low pH.