Ribose-binding protein(RBP) of E. coli functions in transport through permease and in chemotaxis through interaction with chemoreceptor Trg. We isolated transport-defective mutant RBP by using chimeric receptor Trz that has the periplasmic domain of Trg and the cytoplasmic domain of EnvZ. The ribose chemotactic signal is transmitted through Trz to an expression of ompC-lacZ fusion. Mutant RBP was defective in interaction with permease and normal in interaction with Trg. Also, ribose binding (Kd) and protein stability were normal. Mutations were located in the surface of N- domain(52DG, 52DN, 52DN/72GD) or C-domain(134GD, 166RH, 166RC).
Ribose permease, an ABC(ATP-binding Cassette) transporter, in the cytoplasmic membrane is composed of RbsD, RbsA, and RbsC proteins. We isolated suppressors mapped in the permease gene for the tranport mutants by random mutagenesis and screening. The permease suppressors restored ribose transport and swarm phenotype in the presence of mutant RBP. Allele specificity was observed between the suppressor and the original mutations of RBP, suggesting that there are specific areas of contact between the permease components and the domains of RBP.
