Research Publications (Food Safety)

Tilimycin is an enterotoxin produced by the opportunistic pathogen Klebsiella oxytoca that causes antibiotic-associated hemorrhagic colitis (AAHC). This pyrrolobenzodiazepine (PBD) natural product is synthesized by a bimodular nonribosomal peptide synthetase (NRPS) pathway composed of three proteins: NpsA, ThdA, and NpsB.

Bacterial infections are urgent threats to human health, especially in light of rising rates of antibiotic resistance, and their ubiquity demands the development of efficient diagnostic platforms. Electrochemical biosensors for point-of-care testing are garnering interest due to their speed, sensitivity, and selectivity as well as their inexpensive, user-friendly operation. These biosensors have the potential to make significant commercial and clinical impacts.

Ricin toxin A subunit (RTA) removes an adenine from the universally conserved sarcin/ricin loop (SRL) on eukaryotic ribosomes, thereby inhibiting protein synthesis. No high affinity and selective small molecule therapeutic antidotes have been reported against ricin toxicity. RTA binds to the ribosomal P stalk to access the SRL. The interaction anchors RTA to the P protein C-termini at a well-defined hydrophobic pocket, which is on the opposite face relative to the active site.

Chemistry campaigns identified amphiphilic indolyl Mannich bases as novel membrane-permeabilizing antimycobacterials. Spiroketal analogs of this series showed increased potency, and the lead compound 1 displayed efficacy in a mouse model of tuberculosis. Yet the mechanism by which the spiroketal moiety accomplished the potency “jump” remained unknown.

Viridicatumtoxins are a rare class of tetracycline-like antibiotics that strongly inhibit drug-resistant Gram-positive bacteria. Although reported to exhibit in vitro inhibition activity to undecaprenyl pyrophosphate synthase (UPPS), an essential enzyme in bacterial cell wall synthesis, the biological targets and mechanism of action of viridicatumtoxins, especially the drug–target interactions, remain largely unknown.

Cytochrome bd (cyt-bd) oxygen reductases have a high affinity to oxygen and use the two electrons provided by ubiquinol or menaquinol, like in mycobacteria, to reduce oxygen to water. Although they do not pump protons from the cytoplasmic to the periplasmic side, they generate a proton motive force due to the release of protons after quinol oxidation.

Staphylococcus aureus is notoriously known for its rapid development of resistance to conventional antibiotics. S. aureus can alter its membrane composition to reduce the killing effect of antibiotics and antimicrobial peptides (AMPs). To obtain a more complete picture, this study identified the resistance genes of S. aureus in response to human cathelicidin LL-37 peptides by screening the Nebraska Transposon Mutant Library. In total, 24 resistant genes were identified.

Despite a significant decline in morbidity and mortality over the last two decades, in 2018 there were 228 million reported cases of malaria and 405000 malaria-related deaths. Artemisinin, the cornerstone of artemisinin-based combination therapies, is the most potent drug in the antimalarial armamentarium against falciparum malaria. Heme-mediated activation of artemisinin and its derivatives results in widespread parasite protein alkylation, which is thought to lead to parasite death.

Poor patient adherence to antiretroviral medication represents a major obstacle for managing disease and reducing rates of new HIV infections. The measurement of patient drug levels is the most objective method of determining adherence. Tenofovir and tenofovir diphosphate are metabolites of some of the most common HIV medications for treatment and prevention and can be quantified by mass spectrometry.

Promysalin is a small-molecule natural product that specifically inhibits growth of the Gram-negative pathogen Pseudomonas aeruginosa (PA). This activity holds promise in the treatment of multidrug resistant infections found in immunocompromised patients with chronic illnesses, such as cystic fibrosis. In 2015, our lab completed the first total synthesis; subsequent analogue design and SAR investigation enabled identification of succinate dehydrogenase (Sdh) as the biological target in PA.

The Burkholderia cepacia complex is a group of closely related bacterial species with large genomes that infect immunocompromised individuals and those living with cystic fibrosis. Some of these species are found more frequently and cause more severe disease than others, yet metabolomic differences between these have not been described. Furthermore, our understanding of how these species respond to antibiotics is limited.

The emergence and rapid spread of antibiotic resistance poses a serious threat to healthcare systems across the globe. The existence of carbapenemase-producing Enterobacteriaceae (CPE) such as Klebsiella pneumoniae renders the use of carbapenems, the last-resort class of β-lactam antibiotics, ineffective against bacterial infections, often leading to CPE-associated mortalities.

Vibrio cholerae (V. cholerae) uses the autoinducer CAI-1 (cholera autoinducer 1) and several linked quorum sensing systems in order to efficiently sense its ever-changing environment and optimally coordinate population-wide gene expression. Indole has been reported as an important signal that is sensed by V. cholerae, and here, we report the synthesis and evaluation of a focused library of synthetic indole–CAI-1 derivatives as tools to probe quorum sensing (QS) in this human pathogen.

In the course of optimizing a novel indazole sulfonamide series that inhibits β-ketoacyl-ACP synthase (KasA) of Mycobacterium tuberculosis, a mutagenic aniline metabolite was identified. Further lead optimization efforts were therefore dedicated to eliminating this critical liability by removing the embedded aniline moiety or modifying its steric or electronic environment.

Retroviral reverse transcriptases (RTs) have the ability to carry out strand displacement DNA synthesis in the absence of accessory proteins. Although studies with RTs and other DNA polymerases suggest that fingers subdomain residues participate in strand displacement, molecular determinants of this activity are still unknown.

Malaria is a tropical disease that kills about half a million people around the world annually. Enzymatic reactions within pyrimidine biosynthesis have been proven to be essential for Plasmodium proliferation. Here we report on the essentiality of the second enzymatic step of the pyrimidine biosynthesis pathway, catalyzed by aspartate transcarbamoylase (ATC).

The role of molecular arrangement of hydrophobic and hydrophilic groups for designing membrane-active molecules remains largely ambiguous. To explore this aspect, herein we report a series of membrane-active small molecules by varying the spatial distribution of hydrophobic groups.

The emergence and prevalence of carbapenem-resistant bacterial infection have seriously threatened the clinical use of almost all β-lactam antibacterials. The development of effective metallo-β-lactamase (MβL) inhibitors to restore the existing antibiotics efficacy is an ideal alternative. Although several types of serine-β-lactamase inhibitors have been successfully developed and used in clinical settings, MβL inhibitors are not clinically available to date.

The ability to respire and generate adenosine triphosphate (ATP) is essential for the physiology, persistence, and pathogenicity of Mycobacterium tuberculosis, which causes tuberculosis. By employing a lead repurposing strategy, the malarial cytochrome bc1 inhibitor SCR0911 was tested against mycobacteria. Docking studies were carried out to reveal potential binding and to understand the binding interactions with the target, cytochrome bcc.

The nucleocapsid protein (NC) is a highly conserved protein that plays key roles in HIV-1 replication through its nucleic acid chaperone properties mediated by its two zinc fingers and basic residues. NC is a promising target for antiviral therapy, particularly to control viral strains resistant to currently available drugs.

Biofilm inhibition by exogenous molecules has been an attractive strategy for the development of novel therapeutics. We investigated the biofilm inhibitor taurolithocholic acid (TLCA) and its effects on the specialized metabolism, virulence, and biofilm formation of the clinically relevant bacterium Pseudomonas aeruginosa strain PA14. Our study shows that TLCA alters the specialized metabolism, thereby affecting P. aeruginosa colony biofilm physiology.

Antibiotic resistance is a worldwide threat due to the decreasing supply of new antimicrobials. Novel targets and innovative strategies are urgently needed to generate pathbreaking drug compounds. NAD kinase (NADK) is essential for growth in most bacteria, as it supports critical metabolic pathways. Here, we report the discovery of a new class of antibacterials that targets bacterial NADK.

Protein S-palmitoylation is an important post-translational modification (PTM) in blood stages of the malaria parasite, Plasmodium falciparum. S-palmitoylation refers to reversible covalent modification of cysteine residues of proteins by saturated fatty acids.

Despite the high morbidity and mortality of invasive fungal infections (IFIs), effective and safe antifungal agents are rather limited. Starting from antifungal lead compound haloperidol that was identified by drug repurposing, a series of novel benzocyclane derivatives were designed, synthesized, and assayed. Several compounds showed improved antifungal potency and broader antifungal spectra.

LpxD, acyl-ACP-dependent N-acyltransferase, is the third enzyme of lipid A biosynthesis in Gram-negative bacteria. A recent probe-based screen identified several compounds, including 6359-0284 (compound 1), that inhibit the enzymatic activity of Escherichia coli (E. coli) LpxD. Here, we use these inhibitors to chemically validate LpxD as an attractive antibacterial target.