Breakdown in the relationship between thermal and thermodynamic stability in an interleukin-1{beta} point mutant modified in a surface loop |
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Authors: | Chrunyk, Boris A. Wetzel, Ronald |
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Affiliation: | Macromolecular Sciences Department, SmithKline Beecham Pharmaceuticals 709 Swedeland Road, King of Prussia, PA 19406, USA 1Present address: Central Research Division, Pfizer Inc. Eastern Point Rd, Groton, CT 06340, USA |
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Abstract: | Sequence variants of the ß-barrel protein interleukin-1ßhave been analyzed for their stabilities toward irreversiblethermal inactivation by monitoring the generation of light scatteringaggregates on heating. The derived temperatures for the onsetof aggregation (Tagg values) correlate well with the free energiesof unfolding of these proteins with the exception of one variant,Lys97Val (K97V), which undergoes aggregation at a temperature7°C lower than expected based on its thermodynamic stability.This lower than expected thermal stability may be due to generationof an aggregation-prone unfolding intermediate at a temperaturelower than the Tm of the global transition. This hypothesisis supported by the location of residue 97 in the long 8699loop which has structural features suggesting it may comprisea small, independent folding unit or microdomain. The excellentcorrelation of thermal and thermodynamic stabilities of sevenof the eight variants tested is consistent with accepted modelsfor thermal inactivation of proteins. At the same time the poorfit of the K97V variant underscores the risk in using thermalstability data in quantitative analysis of mutational studiesof the folding stability of proteins. |
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Keywords: | aggregation/ microdomain/ unfolding intermediate |
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