The influence of ATP on the binding of aromatic amino acids to the ligand response domain of the tyrosine repressor of Haemophilus influenzae

The binding of aromatic amino acids to the ligand response domain of the ty rosine repressor (TyrR) protein (TyrR(Ird)) Of Haemophilus influenzae was i nvestigated using circular dichroism and fluorescence spectroscopy. The ind uced secondary structural changes were unique for each aromatic amino acid and were further influenced by the presence or absence of ATP. Tyrosine was found to have the highest affinity for TyrR(Ird) in the absence of ATP? wh ereas the affinity for ATP itself increased in the presence of tyrosine. Bi nding of tyrosine is therefore the conformational trigger for the activatio n of TyrR whereas ATP is regarded as a conformational co-activator, (C) 200 0 Federation of European Biochemical Societies.