Comparison of denaturation of tryptophan synthase α-subunits from Escherichia coli, Salmonella typhimurium, and an interspecies hybrid

Abstract

Guanidine hydrochloride-induced denaturation and thermal denaturation of three kinds of tryptophan synthase α subunit have been compared by circular dichroism measurements. The three α subunits are from Escherichia coli, Salmonella typhimurium, and an interspecies hybrid in which the C-terminal domain comes from E. coli (α-2 domain) and the N-terminal domain comes from S. typhimurium (α-1 domain). Analysis of denaturation by guanidine hydrochloride at 25 °C showed that the α-2 domain of S. typhimurium was more stable than the α-2 domain of E. coli, but the α-1 domain of S. typhimurium was less stable than the α-1 domain of the E. coli protein; overall, the hybrid protein was slightly less stable than the two original proteins. It is concluded that the stability to guanidine hydrochloride denaturation of each of the domains of the interspecies hybrid is similar to the stability of the domain of the species from which it originated. The E. coli protein was more stable to thermal denaturation than the other proteins near the denaturation temperature, but the order of their thermal stability was reversed at 25 °C and coincided with that obtained from guanidine hydrochloride-induced denaturation.