FUNCTIONAL-ANALYSIS OF THE PSEUDOMONAS-AERUGINOSA AUTOINDUCER PAI

A series of structural analogs of the Pseudomonas aeruginosa autoinduc er [PAI, N-3-oxo-dodecanoyl homoserine lactone] were obtained and test ed for their ability to act as autoinducers in stimulating the express ion of the gene for elastase (lasB) by measuring beta-galactosidase pr oduction from a lasB-lacZ gene fusion in the presence of the transcrip tional activator LasR. The data suggest that the length of the acyl si de chain of the autoinducer molecule is the most critical factor for a ctivity. Replacement of the ring O by S in the homoserine lactone moie ty can be tolerated. Tritium-labelled PAI ([H-3]PAI) was synthesized a nd used to demonstrate the association of [H-3]PAI with cells overexpr essing LasR. The PAI analogs were also tested for their ability to com pete with [H-3]PAI for binding of LasR. Results from the competition a ssays suggest that once again the length of the acyl side chain appear s to be crucial for antagonist activity. The presence of the 3-oxo moi ety also plays a significant role in binding since analogs which lacke d this moiety were much less effective in blocking binding of [H-3]PAI . All analogs demonstrating competition with PAI in binding to LasR al so exhibited the ability to activate lasB expression, suggesting that they are functional analogs of PAI.