Michael M. Meijler

Vaccination against weight gain

Obesity endangers the lives of millions of people worldwide, through comorbidities such as heart disease, cancers, type 2 diabetes, stroke, arthritis, and major depression. New approaches to control body weight remain a high priority. Vaccines traditionally have been used to protect against infectious diseases and, more recently, for unconventional targets such as drug addiction. Methodologies that could specifically modulate the bioavailability of an endogenous molecule that regulates energy balance might provide a new foundation for treating obesity. Here we show that active vaccination of mature rats with ghrelin immunoconjugates decreases feed efficiency, relative adiposity, and body weight gain in relation to the immune response elicited against ghrelin in its active, acylated form. Three active vaccines based on the 28-aa residue sequence of ghrelin, a gastric endocrine hormone, were used to immunize adult male Wistar rats (n = 17). Synthetic ghrelin analogs were prepared that spanned residues 1–10 [ghrelin (1–10) Ser-3(butanoyl) hapten, Ghr1], 13–28 [ghrelin (13–28) hapten, Ghr2], and 1–28 [ghrelin(1–28) Ser-3(butanoyl) hapten, Ghr3], and included n-butanoyl esters at Ser-3. Groups immunized with Ghr1 or Ghr3 showed greater and more selective plasma binding capacity for the active, Ser-3-(n-octanoyl) form of ghrelin as compared with Ghr2 or keyhole limpet hemocyanin vaccinated controls. Accordingly, they gained less body weight, with sparing of lean mass and preferential reduction of body fat, consistent with reduced circulating leptin levels. The ratio of brain/serum ghrelin levels was lower in rats with strong anti-ghrelin immune responses. Effects were not attributable to nonspecific inflammatory responses. Vaccination against the endogenous hormone ghrelin can slow weight gain in rats by decreasing feed efficiency.

Diazirine based photoaffinity labeling.

Diazirines are among the smallest photoreactive groups that form a reactive carbene upon light irradiation. This feature has been widely utilized in photoaffinity labeling to study ligand-receptor, ligand-enzyme and protein-protein interactions, and in the isolation and identification of unknown proteins. This review summarizes recent advances in the use of diazirines in photoaffinity labeling.

Modulation of Gene Expression via Disruption of NF-κB Signaling by a Bacterial Small Molecule

The control of innate immune responses through activation of the nuclear transcription factor NF-κB is essential for the elimination of invading microbial pathogens. We showed that the bacterial N-(3-oxo-dodecanoyl) homoserine lactone (C12) selectively impairs the regulation of NF-κB functions in activated mammalian cells. The consequence is specific repression of stimulus-mediated induction of NF-κB–responsive genes encoding inflammatory cytokines and other immune regulators. These findings uncover a strategy by which C12-producing opportunistic pathogens, such as Pseudomonas aeruginosa, attenuate the innate immune system to establish and maintain local persistent infection in humans, for example, in cystic fibrosis patients.

Biofuel Cell Controlled by Enzyme Logic Systems

An enzyme-based biofuel cell with a pH-switchable oxygen electrode, controlled by enzyme logic operations processing in situ biochemical input signals, has been developed. Two Boolean logic gates (AND/OR) were assembled from enzyme systems to process biochemical signals and to convert them logically into pH-changes of the solution. The cathode used in the biofuel cell was modified with a polymer-brush functionalized with Os-complex redox species operating as relay units to mediate electron transport between the conductive support and soluble laccase biocatalyzing oxygen reduction. The electrochemical activity of the modified electrode was switchable by alteration of the solution pH value. The electrode was electrochemically mute at pH > 5.5, and it was activated for the bioelectrocatalytic oxygen reduction at pH < 4.5. The sharp transition between the inactive and active states was used to control the electrode activity by external enzymatic systems operating as logic switches in the system. The enzyme logic systems were decreasing the pH value upon appropriate combinations of the biochemical signals corresponding to the AND/OR Boolean logic. Then the pH-switchable electrode was activated for the oxygen reduction, and the entire biofuel cell was switched ON. The biofuel cell was also switched OFF by another biochemical signal which resets the pH value to the original neutral value. The present biofuel cell is the first prototype of a future implantable biofuel cell controlled by complex biochemical reactions to deliver power on-demand responding in a logical way to the physiological needs.

Macromolecular Inhibition of Quorum Sensing : Enzymes, Antibodies, and Beyond

Department of Chemistry and National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Be’er Sheva, Israel; Department of Biomedical Engineering, The Kolff Institute, University Medical Center Groningen and the University of Groningen, Groningen, The Netherlands; and Departments of Chemistry and Immunology & Microbial Science, The Scripps Research Institute, La Jolla, California, USA

N-(3-oxo-acyl)homoserine lactones signal cell activation through a mechanism distinct from the canonical pathogen-associated molecular pattern recognition receptor pathways.

Innate immune system receptors function as sensors of infection and trigger the immune responses through ligand-specific signaling pathways. These ligands are pathogen-associated products, such as components of bacterial walls and viral nuclear acids. A common response to such ligands is the activation of mitogen-activated protein kinase p38, whereas double-stranded viral RNA additionally induces the phosphorylation of eukaryotic translation initiation factor 2α (eIF2α). Here we have shown that p38 and eIF2α phosphorylation represent two biochemical markers of the effects induced by N-(3-oxo-acyl)homoserine lactones, the secreted products of a number of Gram-negative bacteria, including the human opportunistic pathogen Pseudomonas aeruginosa. Furthermore, N-(3-oxo-dodecanoyl)homoserine lactone induced distension of mitochondria and the endoplasmic reticulum as well as c-jun gene transcription. These effects occurred in a wide variety of cell types including alveolar macrophages and bronchial epithelial cells, requiring the structural integrity of the lactone ring motif and its natural stereochemistry. These findings suggest that N-(3-oxo-acyl)homoserine lactones might be recognized by receptors of the innate immune system. However, we provide evidence that N-(3-oxo-dodecanoyl)homoserine lactone-mediated signaling does not require the presence of the canonical innate immune system receptors, Toll-like receptors, or two members of the NLR/Nod/Caterpillar family, Nod1 and Nod2. These data offer a new understanding of the effects of N-(3-oxo-dodecanoyl)homoserine lactone on host cells and its role in persistent airway infections caused by P. aeruginosa.

Defining the Mode of Action of Tetramic Acid Antibacterials Derived from Pseudomonas aeruginosa Quorum Sensing Signals

In nature, bacteria rarely exist as single, isolated entities, but rather as communities comprised of many other species including higher host organisms. To survive in these competitive environments, microorganisms have developed elaborate tactics such as the formation of biofilms and the production of antimicrobial toxins. Recently, it was discovered that the gram-negative bacterium Pseudomonas aeruginosa , an opportunistic human pathogen, produces an antibiotic, 3-(1-hydroxydecylidene)-5-(2-hydroxyethyl)pyrrolidine-2,4-dione (C(12)-TA), derived from one of its quorum sensing molecules. Here, we present a comprehensive study of the expanded spectrum of C(12)-TA antibacterial activity against microbial competitors encountered by P. aeruginosa in nature as well as significant human pathogens. The mechanism of action of C(12)-TA was also elucidated, and C(12)-TA was found to dissipate both the membrane potential and the pH gradient of Gram-positive bacteria, correlating well with cell death. Notably, in stark contrast to its parent molecule 3-oxo-dodecanoyl homoserine lactone (3-oxo-C(12)-HSL), neither activation of cellular stress pathways nor cytotoxicity was observed in human cells treated with C(12)-TA. Our results suggest that the QS machinery of P. aeruginosa has evolved for a dual-function, both to signal others of the same species and also to defend against host immunity and competing bacteria. Because of the broad-spectrum antibacterial activity, established mode of action, lack of rapid resistance development, and tolerance by human cells, the C(12)-TA scaffold may also serve as a new lead compound for the development of antimicrobial therapeutics.

Live Cell Labeling of Native Intracellular Bacterial Receptors Using Aniline-Catalyzed Oxime Ligation

Live cell fluorescent labeling of proteins has become a seminal tool in biology and has led to hallmark discoveries in diverse research areas such as protein trafficking, cell-to-cell interactions, and intracellular network dynamics. One of the main challenges, however, remains the ability to label intracellular proteins using fluorescent ligands with high specificity, all the while retaining viability of the targeted cells. Here, we present the first example of live cell labeling and imaging of an intracellular bacterial receptor involved in cell-to-cell communication (i.e., quorum sensing), using a novel two-step approach involving covalent attachment of a reactive mimic of the primary endogenous Pseudomonas aeruginosa quorum-sensing signal to its receptor, LasR, followed by aniline-catalyzed oxime formation between the modified receptor and a fluorescent BODIPY derivative. Our results indicate that LasR is not distributed evenly throughout the cytoplasmic membrane but is instead concentrated at the poles of the P. aeruginosa cell.

Deeply Inverted Electron-Hole Recombination in a Luminescent Antibody-Stilbene Complex

The blue-emissive antibody EP2-19G2 that has been elicited against trans-stilbene has unprecedented ability to produce bright luminescence and has been used as a biosensor in various applications. We show that the prolonged luminescence is not stilbene fluorescence. Instead, the emissive species is a charge-transfer excited complex of an anionic stilbene and a cationic, parallel π-stacked tryptophan. Upon charge recombination, this complex generates exceptionally bright blue light. Complex formation is enabled by a deeply penetrating ligand-binding pocket, which in turn results from a noncanonical interface between the two variable domains of the antibody.

Inhibition of Pseudomonas aeruginosa quorum sensing by AI-2 analogs.

Autoinducer-2 (AI-2) has been suggested to serve as a universal interspecies quorum sensing signaling molecule. We have synthesized a set of AI-2 analogs with small incremental changes in alkyl substitution on C-2 and evaluated them for their agonistic and antagonistic potential as quorum sensing (QS) attenuators in two different bacterial species: Pseudomonas aeruginosa and Vibrio harveyi. Unexpectedly, several of the analogs were found to function as synergistic QS agonists in V. harveyi, while two of these analogs inhibit QS in P. aeruginosa.