The histidine-binding protein J, a histidine transport component, has two different functional sites
Journal of Biological Chemistry
Previous work from this laboratory has shown that the histidine-binding protein J is a component of the high affinity histidine transport system in Salmonella typhimurium and that it is the product of the hisJ gene. We now present evidence that the J protein has a second type of site, in addition to its histidine-binding site, and that the second site is essential for the J protein to function in transport. The existence of a second functional site had been inferred from the properties of a
... properties of a mutant strain, TA300. This strain has a single mutation in the hisJ gene and produces a J protein with altered electrophoretic mobility in the presence of sodium dodecyl sulfate. The J protein from this strain binds histidine with normal affinity but functions very poorly in histidine transport. We postulate that the J protein from TA300 has been altered at a site other than its histidinebinding site. Possible biochemical functions of this second site are discussed. Properties of TA300 are compared with those of other strains in which histidine-binding by the J protein has been altered.