Determination of a region of the HisJ binding protein involved in the recognition of the membrane complex of the histidine transport system of Salmonella typhimurium.

Site-directed mutagenesis has been utilized to examine the nature of the interaction of the histidine-binding protein (HisJ) with the membrane-bound components of the histidine transport system. In order to examine a region of the HisJ protein involved in the interaction with the membrane components, a number of charged amino acids in the vicinity of the genetically isolated interaction mutant hisJ5625 (R176C) were mutated. It was found that residues Asp171, Arg176, and Asp178 could be independently altered without affecting the histidine-binding affinity of the HisJ protein. However, the alteration of residues Asp171 and Arg176 greatly reduced the interaction of the HisJ protein with the membrane protein complex, whereas altering residue Asp178 had no effect on this interaction. Simultaneously, altering residues Asp183 and Glu184 resulted in a completely defective protein. The ability of a his-J5625 suppressor HisP protein (HisP(T205A)) to suppress the newly created site-directed mutants was also examined. This suppressor demonstrated specificity toward the amino acid present at position 176 and was also able the suppress the mutation created at position 171.