Structural features of L-tryptophan required for activation of TRAP, the trp RNA-binding attenuation protein of Bacillus subtilis.

A filter binding assay was used to determine the structural features of L-tryptophan required for activation of TRAP, the trp RNA-binding attenuation protein of Bacillus subtilis. We examined the ability of L-tryptophan and 26 of its analogs to activate TRAP. Our findings show that TRAP activation by L-tryptophan is highly cooperative. We also observed that TRAP activation is stereospecific; D-tryptophan did not activate. Our results further indicate that the alpha-amino group and the carbonyl moiety of the alpha-carboxyl group of the ligand are required for TRAP activation and that the heterocyclic amino nitrogen of L-tryptophan greatly enhances TRAP activation. We also found that changes at several positions of the indole ring of L-tryptophan resulted in reduced TRAP activation. In addition, indole and 5-methylindole were shown to be effective competitors of L-tryptophan activation of TRAP.