| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系所 === 103 === ATP is an important metabolite found abundantly in cells. Except being as energy source, it was recently found that ATP also plays as a chemical chaperone to facilitate the folding of an important enzyme, Escherichia coli glyceraldehyde-3-phosphate dehydrogenase. This novel function of ATP is granted by the specific interaction to partially unfolded protein conformation. However, it is still unclear if this chaperone role is unique between ATP and Escherichia coli glyceraldehyde-3-phosphate dehydrogenase. To answer this question, we investigated the interaction between ATP and another protein, Escherichia coli uridine phosphorylase.
Unfolding equilibrium of this protein was measured by pulse proteolysis and tryptophan fluorescence. The results both showed the same apparently destabilizing effect in the presence of 3 mM ATP. Interestingly, ATP decreased Cm value with two transitions that are only monitored by tryptophan fluorescence. This difference compared to pulse proteolysis suggests the possible change of protein quaternary structure. The folding and unfolding kinetics of this protein were also determined. The results show that ATP only accelerates the unfolding but folding rates. This result was confirmed with the activity assay during the refolding of uridine phosphorylase. Moreover, the specificity test also showed decreased stability in the presence of other nucleotides.
In summary, ATP plays a different role on the folding of Escherichia coli uridine phosphorylase. This interaction may be significant to the change of turnover rate or function of this protein.
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