Alkali induced unique partially folded state of bovine serum albumin: qualitative and quantitative insights.

Qualitative and quantitative understanding of partially folded states of protein is essential in gaining deeper insights into folding pathways. We have observed a partially folded state of bovine serum albumin (BSA) in the presence of 2,2,2-trifluoroethanol at pH11.2 which does not resembles the properties of the molten globule state. ThT, a frequently used marker for protein fibrils have two order of greater affinity towards the intermediate state at pH11.2 compared to native BSA at pH7.4. Surprisingly, the binding of ANS with this partially folded state is weaker than that of native state of BSA. Combined fluorescence, circular dichroism spectroscopy and isothermal titration calorimetric studies indicate that for such partially folded state, ThT is a better marker compared to ANS. The results have highlighted the importance of dyes like ThT in characterizing partilally folded states of protein which might appear as intermediates in the funnel moldel describing the protein folding pathway.