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2). and food poisoning to life-threatening nosocomial infections. Increasing resistance of isolates to glycopeptide antibiotics, most prominently vancomycin, is a major concern in todays intensive care units, therefore, an alternative strategy to combat this pathogen is urgently required. (system utilizes cyclic oligopeptides, termed autoinducing peptide (AIP), and these contribute to bacterial pathogenesis by orchestrating the temporal cell density-dependent expression of virulence genes [22]. Genes regulated by encode cell surface proteins such as protein A, coagulase, fibronectin-binding proteins; secreted proteins including proteases, hemolysins, toxic shock syndrome toxin 1 (TSST-1), and enterotoxin B. In addition, the QS system has also been linked to resistance with glycopeptide antibiotics in [23]. Notably, Novick and co-workers have demonstrated that transient inactivation of the QS circuit might indeed be sufficient to prevent the deleterious effects of certain infections [24]. Thus far, four different AIPs, with varying degrees of sequence similarities have been identified as QS molecules (Fig. 1) [25]. As a starting point for antibody-based interference with AIP-mediated QS, we focused on the AIP-4 QS system and its cognate strains RN4850 and NRS168 [16]. Open in a separate window Figure 1 Structures of the AIPs used by a thioester linkage between the thiol moiety of the conserved (*)Cys and the carboxyl group of the C-terminal residue. Results DCVC and Conversation Design and Synthesis of AIP-4 Hapten Based on the reported structural info of AIP-4 [26], we designed and synthesized the hapten AP4-5 to elicit an anti-AIP-4 antibody immune response in mice (Fig. 2). Our reasoning for the chemical switch from your native thiolactone to a lactone-containing hapten was based on a lactones higher aminolytic stability [27]. This strategy guaranteed the hapten conjugates remained structurally undamaged during the immunization process and subsequent immune response; thus, avoiding the generation of degradation products with unknown chemical and biological properties as previously uncovered for additional QS molecules by our laboratory [28]. Furthermore, this substitution was also intended Rabbit polyclonal to DCP2 to prevent a possible intramolecular thiol exchange between the conserved thiolactone and the pendant cysteine thiol. Consequently, Fmoc-Serine(Trt)-OH was integrated at position 4 in place of the native cysteine residue. Open in a separate window Number 2 Synthesis of the AP4 hapten 5The linear peptide was synthesized on 2-chlorotrityl resin preloaded with Fmoc-Methionine 1 using standard Fmoc chemistry utilizing DIC/HOBt as coupling reagents. The N-terminal pendant cysteine was integrated for conjugation to a carrier protein and the short flexible linker was added DCVC between the hapten and the carrier protein as spacer. The safeguarded linear peptide was released from your resin using 4% trifluoroacetic acid in chloroform, which also selectively eliminated the trityl safety group from your serine. Intramolecular lactonization under dilute conditions was performed using EDC/4-DMAP, and subsequent side chain deprotections afforded the AP4 hapten 5. (For full details, observe Experimental Methods). The hapten 5 was conjugated DCVC to the carrier proteins keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) via a bifunctional linker (observe Supplemental Fig. 1). Balb/c mice were immunized with the KLH conjugate using standard protocols [19]. Overall, the immunizations resulted in moderate titers (1600 – 3200), and based on ELISA analysis, 20 monoclonal antibodies (mAbs) were prepared. The affinities of the AP4-mAbs were determined against all four natural AIPs using competition ELISA strategy (observe Supplemental Table 1). One of the mAbs, namely AP4-24H11, possessed strong binding affinity (Kd AIP-4 90 nM) and high specificity to AIP-4 while showing little mix reactivity for the additional AIPs (Kd AIP-1 5 M, Kd AIP-2 = >25 M, Kd AIP-3 = >25 M). The ability of AP4-24H11 to discriminate between DCVC AIP1 and AIP4 is definitely noteworthy as these two oligopeptides differ only at position 5.