The Trg transducer of E. coli, located in cytoplasmic membrane mediates attractant response to ribose. The periplasmic ribose binding protein (RBP) is encoded by rbsB gene and is thought to interact with Trg transducer. Ligand-occupied ribose-binding protein is supposed to elicit chemotatic response by binding to the Trg transducer and to transport ribose into the cytoplasm.
To study the interaction of RBP with Trg transducer, we used trg mutations that have specific defects in chemotactic response to ribose and wild type trg. pAI12 plasmid containing rbsB gene was with mutagenized hydroxylamine. The mutagenized rbsB plasmids were introduced into the strains that have the trg mutation and then ribose taxis positive transformants were screened on ribose swarm plate. Five suppressors that restore ribose taxis have been isolated. Two of the mutations were sequenced by DNA sequencing to find their mutational changes. One has Glu 192 Lys change and the other Pro 65 Ser. These results suggest that the residues of 65 and 192 of RBP are important for the interaction with Trg transducer.
In addition four ribose-taxis defective RBP mutants were isolated by hydroxylamine mutagenesis and screening on ribose minimal swarm plates. They exhibited reduced tactic responses to ribose in varying degree.
The structural role and significance of these residues in receptor interaction are discussed based on their location in three dimensional structure of RBP generated by computer modelling.