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 between β4 and β5, was substituted with the Arg present in the corresponding position in Bacillus acidocaldarius thioredoxin. This suggested that it could play an important role in the structure and thermostability of this protein owing to its involvement in numerous interactions. The effects of the mutation on the biophysical properties were analysed by circular dichroism, spectrofluorimetry and limited proteolysis, supported by molecular dynamics data. As modelling predicted, an increase in stability for E85R due to additional H-bonds between the β5 and α4 regions was observed.