Immunomodulation and the quorum sensing molecule 3-oxo-C12-homoserine lactone: the importance of chemical scaffolding for probe development

β-Lactams from the Ocean

The title of this essay is as much a question as it is a statement. The discovery of the β-lactam antibiotics-including penicillins, cephalosporins, and carbapenems-as largely (if not exclusively) secondary metabolites of terrestrial fungi and bacteria, transformed modern medicine. The antibiotic β-lactams inactivate essential enzymes of bacterial cell-wall biosynthesis. Moreover, the ability of the β-lactams to function as enzyme inhibitors is of such great medical value, that inhibitors of the enzymes which degrade hydrolytically the β-lactams, the β-lactamases, have equal value. Given this privileged status for the β-lactam ring, it is therefore a disappointment that the exemplification of this ring in marine secondary metabolites is sparse. It may be that biologically active marine β-lactams are there, and simply have yet to be encountered. In this report, we posit a second explanation: that the value of the β-lactam to secure an ecological advantage in the marine environment might be compromised by its close structural similarity to the β-lactones of quorum sensing. The steric and reactivity similarities between the β-lactams and the β-lactones represent an outside-of-the-box opportunity for correlating new structures and new enzyme targets for the discovery of compelling biological activities.

Immunoediting role for major vault protein in apoptotic signaling induced by bacterial N-acyl homoserine lactones

The major vault protein (MVP) mediates diverse cellular responses, including cancer cell resistance to chemotherapy and protection against inflammatory responses to Pseudomonas aeruginosa Here, we report the use of photoactive probes to identify MVP as a target of the N-(3-oxo-dodecanoyl) homoserine lactone (C12), a quorum sensing signal of certain proteobacteria including P. aeruginosa. A treatment of normal and cancer cells with C12 or other N-acyl homoserine lactones (AHLs) results in rapid translocation of MVP into lipid raft (LR) membrane fractions. Like AHLs, inflammatory stimuli also induce LR-localization of MVP, but the C12 stimulation reprograms (functionalizes) bioactivity of the plasma membrane by recruiting death receptors, their apoptotic adaptors, and caspase-8 into LR. These functionalized membranes control AHL-induced signaling processes, in that MVP adjusts the protein kinase p38 pathway to attenuate programmed cell death. Since MVP is the structural core of large particles termed vaults, our findings suggest a mechanism in which MVP vaults act as sentinels that fine-tune inflammation-activated processes such as apoptotic signaling mediated by immunosurveillance cytokines including tumor necrosis factor-related apoptosis inducing ligand (TRAIL).

[Microbial dormancy and prevention of healthcare-associated infections]

Healthcare-associated infections (HCAI) remain one of the most challenges of modern health care and assume increasing social and medical significance. The specific features of HCAI are frequent recurrences and inefficiency of antibiotic therapy, a reason for which is antibiotic resistance in microorganisms. The review discusses antibiotic resistance, a form of antibiotic tolerance (AT), and its role in the development of HCAI. It also describes essential differences between AT and antibiotic tolerance at the cellular and molecular genetic levels. Relationships between AT and dormancy of microorganisms, pathogens of HCAI, are discussed. The paper gives the data available in the literature on how AT occurs in HCAI pathogens and discusses the diagnosis of this condition. It also analyzes the literature data on pharmacological attempts to overcome AT and discusses novel approaches to antibiotic therapy for HCAI.