A study of AroP-PheP chimeric proteins and identification of a residue involved in tryptophan transport

In vivo recombination has been used to make a series of AroP-PheP chimeric proteins. Analysis of their respective substrate profiles and activities ha s identified a small region within span III of AroP which can confer on a p redominantly PheP protein the ability to transport tryptophan. Site-directe d mutagenesis of the AroP-PheP chimera, PheP, and AroP has established that a key residue involved in tryptophan transport is tyrosine at position 103 in AroP. Phenylalanine is the residue at the corresponding position in Phe P. The use of PheP-specific antisera has shown that the inability of certai n chimeras to transport any of the aromatic amino acids is not a result of instability or a failure to be inserted into the membrane. Site-directed mu tagenesis has identified two significant AroP-specific residues, alanine 10 7 and valine 114, which are the direct cause of loss of transport activity in chimeras such as A152P. These residues replace a glycine and an alanine in PheP and Bank a highly conserved glutamate at position 110. Some suggest ions are made as to the possible functions of these residues in the tertiar y structure of the proteins.