The transparency of the eye lens depends on the high solubility and stability of the lens crystallin proteins. The monomeric gamma-crystallins and oligomeric beta-crystallins have paired homologous double Greek key domains, presumably evolved through gene duplication and fusion. Prior investigation of the refolding of human gammaD-crystallin revealed that the C-terminal domain folds first and nucleates the folding of the N-terminal domain. This result suggested that the human N-terminal domain might not be able to fold on its own. We constructed and expressed polypeptide chains corresponding to the isolated N- and C-terminal domains of human gammaD-crystallin, as well as the isolated domains of human gammaS-crystallin. Both circular dichroism and fluorescence spectroscopy indicated that the isolated domains purified from Escherichia coli were folded into native-like monomers. After denaturation, the isolated domains refolded efficiently at pH 7 and 37 degrees C into native-like structures. The in vitro refolding of all four domains revealed two kinetic phases, identifying partially folded intermediates for the Greek key motifs. When subjected to thermal denaturation, the isolated N-terminal domains were less stable than the full-length proteins and less stable than the C-terminal domains, and this was confirmed in equilibrium unfolding/refolding experiments. The decrease in stability of the N-terminal domain of human gammaD-crystallin with respect to the complete protein indicated that the interdomain interface contributes of 4.2 kcal/mol to the overall stability of this very long-lived protein. Study holds ProTherm entries: 23707, 23708, 23709, 23710, 23711, 23712 Extra Details: human gammaD-crystallin; human gammaS-crystallin; domain interface; cataract; equilibrium unfolding/refolding transitions; refolding kinetic intermediates; protein stability
Submitter: Connie Wang
Submission Date: April 24, 2018, 8:54 p.m.
|Number of data points||12|
|Proteins||Beta-crystallin S ; Beta-crystallin S|
|Assays/Quantities/Protocols||Experimental Assay: Cm ; Experimental Assay: m ; Experimental Assay: dG_H2O ; Experimental Assay: Tm|
|Libraries||Mutations for sequence GQYKIQIFEKGDFSGQMYETTEDCPSIMEQFHMREIHSCKVLEGVWIFYELPNYRGRQYLLDKKEYRKPIDWGAASPAVQSFRRIVE|