Hybrid tryptophan synthase beta 2 proteins: apparent conservation of the beta-beta binding region of the beta monomer among enteric bacteria

Purified borohydride-reduced tryptophan synthase beta 2 protein (EC 4.2.1.20) from Escherichia coli and purified native beta 2 protein from Serratia marcescens were mixed and dissociated in urea. Removal of the urea resulted in random reassociation of the reduced and native beta monomers, forming interspecies hybrid beta 2 molecules. Interspecies hybrid beta 2 protein molecules of the reciprocal composition were also formed. Interspecies hybrid reconstituted molecules were formed with approximately the same efficiency as intraspecies reconstituted molecules (reduced and native monomers from the same species) indicating no particular preference for reassembly. The data provide evidence that the structural region of interaction between the beta monomers necessary for dimerization is highly conserved in the enzymes from the two organisms examined.