Chemical denaturants induced folding unfolding pathway of the recombinant zebrafish dihydrofolate reductase

Denaturation of proteins plays a crucial part in cellular activities. In this study, we have investigated the folding unfolding pathways of zebrafish dihydrofolate reductase (zDHFR) in presence of different chemical denaturants which were found to be an influential factor for the refolding yield by UV-visible spectrophotometric analysis. The activity change of zDHFR has been observed in presence of three different denaturants like Acetic Acid (AcOH), Sodium Dodecyl Sulphate (SDS), and Ethanol (C2H5OH). Spectrophotometric analysis reveals that protein unfolded completely at different concentrations and times by these denaturants. The spontaneous refolding experiments of chemically denatured zDHFR were also conducted to verify the spontaneous refolding yield. These investigations have helped us to decipher a picture about the denaturants contributing to achieving the refolding yield. We observed that acetic acid is a stronger denaturant among all, and the spontaneous refolding yields were higher from SDS denaturation. In the light of the above findings, higher spontaneous refolding yields were obtained from the low concentration of denaturants.

Allosteric serine hydroxymethyltransferase from monkey liver: Correlation of conformational changes caused by denaturants with the alterations in catalytic activity.

The far-ultraviolet region circular dichroic spectrumof serine hydroxymethyltransferase from monkey liver showed that the protein is in an α-helical conformation. The near ultraviolet circular dichoric spectrum revealed two negative bands originating from the tertiary conformational environment of the aromatic amino acid residues. Addition of urea or guanidinium chloride perturbed the characteristic fluorescence and far ultraviolet circular dichroic spectrum of the enzyme. The decrease in (θ)222 and enzyme activity followed identical patterns with increasing concentrations of urea, whereas with guanidinium chloride, the loss of enzyme activity preceded the loss of secondary structure. 2-Chloroethanol, trifluoroethanol and sodium dodecyl sulphate enhanced the mean residue ellipticity values. In addition, sodium dodecyl sulphate also caused a perturbation of the fluorescence emission spectrum of the enzyme. Extremes of pH decreased the – (θ)222 value. Plots of –(θ)222and enzyme activity as a function of pH showed maximal values at pH 7.4-7.5. These results suggested the prevalence of "conformational flexibility" in the structure of serine hydroxymethyltransferase.