| Abstract
| - Site-directed mutagenesis of the aspartate receptor ofSalmonella typhimurium(TarS)1 at serine68, a residue located within the aspartate binding pocket and at thesubunit interface, identified this residueas an allosteric switch in this receptor. Substitutions at thisposition can affect both the type and degreeof binding cooperativity observed. Negative cooperativity isobserved in the wild-type receptor (nH=0.7 ± 0.1) and is maintained by the mutations S68C(nH = 0.8 ± 0.02), S68V(nH = 0.9 ± 0.05), andS68D (half-of-the-sites). Binding at only half of the sites wasdetectable in the S68D mutant, an extremeform of negative cooperativity. No cooperativity(nH = 1.0 ± 0.03) was observed in the mutantS68A.Positive cooperativity was generated by the substitutions S68T(nH = 1.2 ± 0.09), S68L(nH = 1.2 ±0.1), S68N (nH = 1.3 ± 0.2), and S68I(nH = 1.4 ± 0.2). Binding measurementsindicated that thesubstitutions S68Q, S68E, and S68F decrease affinity of the firstligand binding 500-fold, 7000-fold, and1600-fold, respectively.
|
