Question

Protein Structure Evaluation Based on Gel Filtration Data A new protein of unknown structure has been purified. Gel filtration chromatography reveals that the native protein has a molecular weight of 240,000. Chromatography in the presence of 6 M guanidine hydrochloride yields a single peak corresponding to a protein of Mr 60,000. Chromatography in the presence of 6 M guanidine hydrochloride and 10 mM b-mercaptoethan yield peaks for protein of Mr 34,000 and 26,000. Explain what can be determined about the structure of this protein from these data?

Answer 1

Based on the given information, the disruption of hydrogen bonds and other weak forces that helps in integrating the structure of the protein is mediated by guanidine hydrochloride, that is, it denatures the protein. Only a solitary peak of Mr 60000 is witnessed post denaturation. This clearly shows that only one peptide of Mr 60000 is left in the solution post denaturation.

Of the entire protein of molecular weight 240000 D, post denaturation only the protein of 60000 D got left, which shows that the protein comprises four subunits of 60000 D, and thus, is a tetramer.

With the addition of 10 mM beta-mercaptoethanol, the protein got further dissociated into two subunits of molecular weight 34000 D and 26000 D showing that each subunit of protein was linked by disulfide bonds, which got broken with the addition of beta-mercaptoethanol.