Structure of the periplasmic glucose/galactose receptor of Salmonella typhimurium.

The X-ray structure of the periplasmic glucose/galactose receptor (binding protein) of Salmonella typhimurium has been solved by the method of multiple isomorphous replacement and refined to a resolution of 2.4 A with an R-factor of 15.8%. The protein consists of two highly-similar structural domains with a bound sugar molecule trapped between. A combined sequence/structural approach is used to compare the structure of this protein to a similar arabinose receptor. The new sequence alignment obtained is used to analyze a number of features conserved for structural and functional reasons. This information allowed the prediction of similar features within the sequence of the analogous ribose receptor. Some of the consequences of the structures for chemotaxis and transport are discussed.