Mussels adhere to a variety of surfaces by depositing a highly specific ensemble of 3,4-dihydroxyphenyl-L-alanine (DOPA) containing proteins. The adhesive properties of Mytilus edulis foot proteins mfp-1 and mfp-3 were directly measured at the nano-scale by using a surface forces apparatus (SFA). An adhesion energy of order W Ϸ3 ؋ 10 ؊4 J/m 2 was achieved when separating two smooth and chemically inert surfaces of mica (a common alumino-silicate clay mineral) bridged or ''glued'' by mfp-3. This energy corresponds to an approximate force per plaque of Ϸ100 gm, more than enough to hold a mussel in place if no peeling occurs. In contrast, no adhesion was detected between mica surfaces bridged by mfp-1. AFM imaging and SFA experiments showed that mfp-1 can adhere well to one mica surface, but is unable to then link to another (unless sheared), even after prolonged contact time or increased load (pressure). Although mechanistic explanations for the different behaviors are not yet possible, the results are consistent with the apparent function of the proteins, i.e., mfp-1 is disposed as a ''protective'' coating, and mfp-3 as the adhesive or ''glue'' that binds mussels to surfaces. The results suggest that the adhesion on mica is due to weak physical interactions rather than chemical bonding, and that the strong adhesion forces of plaques arise as a consequence of their geometry (e.g., their inability to be peeled off) rather than a high intrinsic surface or adhesion energy, W.
bioadhesion ͉ Mytilus edulis
Bacterial quorum sensing is mediated by low molecular-weight signals and plays a critical role in both the pathogenesis of infectious disease and beneficial symbioses. There is significant interest in the development of synthetic ligands that can intercept bacterial quorum sensing signals and modulate these outcomes. Here, we report the design and comparative analysis of the effects of ~ 90 synthetic N-acylated homoserine lactones (AHLs) on quorum sensing in three Gram negative bacterial species and a critical examination of the structural features of these ligands that dictate agonistic and antagonistic activity, and selectivity for different R protein targets. These studies have revealed the most comprehensive set of structure-activity relationships to date that direct AHL-mediated quorum sensing and a new set of chemical probes with which to study this complex signaling process. Furthermore, this work provides a foundation on which to design next-generation quorum sensing modulators with improved activities and selectivities.
1, 8-Naphthalimide, as one of the classical dyes and fluorophores, has been widely used in the analytical chemistry, material chemistry and biochemistry field because of its excellent characteristics photostability, good...
Quorum sensing (QS) is under the control of N-acylated L-homoserine lactones (AHLs) and their cognate receptors (LuxR-type proteins) in Gram-negative bacteria, and plays a major role in mediating host-bacteria interactions by these species. Certain cyclic dipeptides (2,5-diketopiperazines, DKPs) have been isolated from bacteria and reported to activate or inhibit LuxRtype proteins in AHL biosensor strains, albeit at significantly higher concentrations than native lactones. These reports have prompted the proposal that DKPs represent a new class of QS signals, and potentially even interspecies or interkingdom signals; their mechanisms of action and physiological relevance, however, remain unknown. Here, we describe a library of synthetic DKPs that was designed to (1) determine the structural features necessary for LuxR-type protein activation and inhibition, and (2) probe their mechanisms of action. These DKPs, along with several previously reported natural DKPs, were screened in bacterial reporter gene assays. In contrast to previous reports, the native DKPs failed to exhibit either antagonistic or agonistic activities in these assays. However, non-natural halogenated cyclo(L-Pro-L-Phe) derivatives were capable of inhibiting luminescence in V. fischeri. Interestingly, additional experiments revealed that these DKPs do not compete with the natural lactone signal, OHHL, to inhibit luminescence. Together, these data suggest that DKPs are not QS signals in the bacteria examined in this study. Although these compounds can influence QS-regulated outcomes, we contend that they do not do so through direct interaction with LuxR-type proteins. This work serves to refine the lexicon of naturally occurring QS signals used by Gram-negative bacteria.
A supramolecular-gel-based twenty-two-member sensor array has been created by introducing well-designed multi-competitive binding interactions into a supramolecular gel.
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