Probing Autoinducer-2 Based Quorum Sensing: The Biological Consequences of Molecules Unable To Traverse Equilibrium States

Abstract

Bacteria have developed a cell-to-cell communication system, termed quorum sensing (QS), which allows for the population-dependent coordination of their behavior via the exchange of chemical signals. Autoinducer-2 (AI-2), a class of QS signals derived from 4,5-dihydroxy-2,3-pentandione (DPD), has been revealed as a universal signaling molecule in a variety of bacterial species. In spite of the considerable interest, the study of putative AI-2 based QS systems remains a challenging topic in part due to the rapid interconversion between the linear and cyclic forms of DPD. Herein, we report the design and development of efficient syntheses of carbocyclic analogues of DPD, which are locked in the cyclic form. The synthetic analogues were evaluated for the modulation of AI-2 based QS in Vibrio harveyi and Salmonella typhimurium. No agonists were uncovered in either V. harveyi or S. typhimurium assay, whereas weak to moderate antagonists were found against V. harveyi. Based on NMR analyses and DFT calculations, the heterocyclic oxygen atom within DPD appears necessary to promote hydration at the C3 position of cyclic DPD to afford the active tetrahydroxy species. These results also shed light on the interaction between the heterocyclic oxygen atom and receptor proteins as well as the importance of the linear form and dynamic equilibrium of DPD as crucial requirements for activation of AI-2 based QS circuits.

Dissecting AI-2-mediated quorum sensing through C5-analogue synthesis and biochemical analysis

“…As with all α-diketone DPD analogues, the final acid-catalysed deprotection was carried out without purification or concentration of the resulting solution; it has previously been shown that the tert -butyldimethylsilanol by-product is non-toxic and inactive up to 100 µM against both V. harveyi and S. Typhimurium. 7 …”

“…2 We have previously investigated the use of carbocyclic analogues to mimic fixed ring-closed conformations of DPD (DHMP and triHMP, Figure 2). 7 However, the direct analogue DHMP had no significant effect against either V. harveyi or S. Typhimurium, and triHMP showed only limited antagonism in V. harveyi . DFT calculations suggested limited hydration at the C3 ketone of DHMP, a requirement for formation of the borate diester.…”

Interspecific Quorum Sensing Mediates the Resuscitation of Viable but Nonculturable Vibrios

“…VBNC cultures were prepared as described above. The synthetic autoinducer (s)-4,5-dihydroxy-2,3-pentanedione (DPD) (OMM Scientific, Dallas, TX) spontaneously forms the quorum sensing molecule AI-2 in liquid suspension (31). AI-2 was prepared by adding a 10-fold molar excess of boric acid to DPD, making a 50 M DPD stock solution.…”

Strategies for Silencing Bacterial Communication

“…The activity of these multiple C1-alkyl-DPD derivatives in V. harveyi depended on the assay conditions; they were found to function as either antagonists or synergistic agonists (LaSarre and Federle 2013; Defoirdt et al 2012;Lowery et al 2008). However, carbocyclic analogues of DPD did not display significant quenching activities in S. typhimurium or V. harveyi (Tsuchikama et al 2011;Guo et al 2013). Generally, AI-2 QS antagonists can exhibit two different types of activities being antagonists or synergistic agonists (LaSarre and Federle 2013).…”