Effects of hydroxyl group in cyclo(Pro-Tyr)-like cyclic dipeptides on their anti-QS activity and self-assembly.

We investigated the influence of hydroxyl groups on the anti-quorum-sensing (anti-QS) and anti-biofilm activity of structurally similar cyclic dipeptides, namely cyclo( L -Pro- L -Tyr), cyclo( L -Hyp- L -Tyr), and cyclo( L -Pro- L -Phe), against Pseudomonas aeruginosa PAO1. Cyclo( L -Pro- L -Phe), lacking hydroxyl groups, displayed higher virulence factor inhibition and cytotoxicity, but showed less inhibitory ability in biofilm formation. Cyclo( L -Pro- L -Tyr) and cyclo( L -Hyp- L -Tyr) suppressed genes in both the las and rh l systems, whereas cyclo( L -Pro- L -Phe) mainly downregulated rhl I and pqs R expression. These cyclic dipeptides interacted with the QS-related protein LasR, with similar binding efficiency to the autoinducer 3OC12-HSL, except for cyclo( L -Pro- L -Phe) which had lower affinity. In addition, the introduction of hydroxyl groups significantly improved the self-assembly ability of these peptides. Both cyclo( L -Pro- L -Tyr) and cyclo( L -Hyp- L -Tyr) formed assembly particles at the highest tested concentration. The findings revealed the structure-function relationship of this kind of cyclic dipeptides and provided basis for our follow-up research in the design and modification of anti-QS compounds.