A single point mutation (Glu85Arg) increases the stability of the thioredoxin from Escherichia coli

Glu85 in the Escherichia coli thioredoxin, which is localized in the loop b etween beta4 and beta5, was substituted with the Arg present in the corresp onding position in Bacillus acidocaldarius thioredoxin. This suggested that it could play an important role in the structure and thermostability of th is protein owing to its involvement in numerous interactions. The effects o f the mutation on the biophysical properties were analysed by circular dich roism, spectro-fluorimetry and limited proteolysis, supported by molecular dynamics data. As modelling predicted, an increase in stability for E85R du e to additional H-bonds between the beta5 and alpha4 regions was observed.