Two periplasmic transport proteins which interact with a common membrane receptor show extensive homology: complete nucleotide sequences.

Abstract

The hisJ and argT genes of Salmonella typhimurium encode 2 periplasmic binding proteins, J and LAO, which are involved in histidine and arginine transport, respectively, and which interact with a common membrane-bound component, the P protein. The complete nucleotide sequences of these 2 genes were determined. The 2 genes show extensive homology (70%) and presumably arose by tandem duplication of a single ancestral gene. The 2 encoded proteins now perform distinct functions but still retain sufficient homology to permit interaction with the same site on the membrane-bound P protein. The distribution of amino acid differences between the 2 proteins; the properties of a functional chimeric protein, produced by a deletion mutant in which the 1st half of the argT gene is fused to the 2nd half of the hisJ gene; and the sequence change in a mutant J protein unable to interact with P allowed the amino acid-binding site and the site involved in the interaction with the P protein to be assigned to specific regions of each binding protein.