Leonhard Hagen Urner

Cationic membrane-active drugs are an important focus of antibiotic research, yet their potential is often limited by poor selectivity. Here, we establish steric protection of cations by modular triethylene glycol as a chemical design framework to decouple antimicrobial potency from cytotoxicity. Using antipsychotics, a class of widely prescribed membrane-active drugs, we show that lipophilicity and rigidity jointly govern antimicrobial potency and mammalian cell cytotoxicity. Membrane perturbation emerged as a key determinant of bioactivity and revealed physicochemical windows that decouple antimicrobial potency and cytotoxicity. Our findings spotlight octanol as a design motif for steric protection of cations that emerged from systematic tuning of side chain lipophilicity and mimics a known metabolite motif. As exemplified with the model drug chlorpromazine, this modification can maintain water solubility, improve membrane engagement, reduce mammalian cell cytotoxicity, enhance antibacterial potency, and amplify polymyxin amplification across Gram-negative bacteria, including drug-resistant clinical isolates. Our findings indicate that membrane remodeling associated with polymyxin resistance in Escherichia coli correlates with a collateral vulnerability to cationic amphiphiles, suggesting a physicochemically tractable consequence of resistance. These findings establish a chemical design framework for small-molecule cationic amphiphiles with improved physicochemical properties, membrane engagement, and bioactivity that can be difficult to achieve by traditional alkylation.

Cationic amphiphiles are investigated as antibacterials, yet their potential is often limited by host-cell toxicity. Bacterial and mammalian membranes share core physicochemical features that promote interactions with cationic amphiphiles. Selectivity is realistically understood as a relative property window. This review summarizes recent trends in the design of antibacterial cationic amphiphiles, focusing on quaternary ammonium compounds, lipopeptides and dendritic amphiphiles. Across these structurally diverse compound classes, tuning charge density, hydrophobicity, degradability, lipid selectivity, and supramolecular properties emerge as design approaches to improve antibacterial potency and reduce toxicity. Recent developments exploit bacterial lipids and lipid membrane surfaces as targets and employ design strategies to improve selectivity, such as multivalent presentation of cationic groups, optimization of membrane insertion, and combinations of membrane-targeting building blocks. Cationic amphiphiles inserting into bacterial membranes can induce permeabilization, dissipation of the proton motive force, and disruption of energy homeostasis, suggesting these processes represent a common mechanistic framework linking physical membrane damage to antibacterial activity. Complementing phenotypic screenings by mechanistic studies and concentration-dependent mode-of-action profiling across compound series is a promising future direction. Understanding how molecular structure governs membrane interactions and bacterial physiology will support the development of next-generation cationic amphiphiles with improved potency, selectivity and translational potential.

The water solubility of hydrophobic amine drugs is pivotal for oral bioavailability and routinely secured by hydrochloride salt formation. In the case of the antipsychotic chlorpromazine, this approach yields a cationic amphiphile with antibacterial potency, which correlates with alterations in gut microbiota. It remains to be clarified whether a covalent conjugation of chlorpromazine to a detergent, as an alternative solubilization strategy, can improve its water solubility and reduce its antibacterial potency. Here, we leverage the modular nature of an asymmetric hybrid detergent to generate a covalent chlorpromazine–detergent conjugate and evaluate its solubility and biological activity. The covalent solubilization strategy improves aqueous solubility relative to supramolecular nanocarriers and decouples drug solubility from antibacterial activity. Detergent conjugation confers solubility and membrane-permeabilizing potency, which correlates with similar cytotoxicity and reduced antibacterial potency compared to chlorpromazine hydrochloride. Collectively, our findings establish a covalent detergent solubilization strategy for hydrophobic amine drugs, provide a rationale for cytotoxicity and antibacterial activity, and highlight its potential for improving solubility and reducing potency against bacteria relevant for gut microbiota.

Gram-negative bacteria are intrinsically resistant to many antibiotics because of densely packed lipopolysaccharides (LPS) in the outer leaflet of their outer membrane (OM), which acts as a highly effective barrier towards the spontaneous permeation of toxic molecules, including antibiotics. LPS are extracted from the inner membrane by the ABC transporter LptB ₂ FGC and translocated across the periplasm via a protein bridge to the OM. While structural studies have elucidated aspects of Lpt function in enterobacteria, little is known about how this system operates in divergent species such as Pseudomonas aeruginosa , a major human pathogen. Here, we report five cryo-electron microscopy structures of P. aeruginosa LptB ₂ FG and LptB ₂ FGC, revealing a rigid body movement in the periplasmic β-jellyroll domains necessary for LPS to shuttle through the periplasmic space. Notably, these structures exhibit a significantly smaller LPS binding cavity compared to previously determined models, suggesting the ligand-unbound states of the transporter. Mass spectrometry and molecular dynamics simulations indicate that the phosphate groups of LPS are the key determinants for binding and that the transporter can also accommodate cardiolipin. Together, these findings reveal previously unappreciated structural diversity in the Lpt system and provide mechanistic insight into how pathogenic Gram-negative bacteria tailor LPS recognition and transport. This understanding offers new avenues for the development of novel inhibitors targeting membrane biogenesis.

Research and applications relevant to human health are enabled by detergent chemistry. A multifaceted overview of this field is yet missing. To close this gap, this topical collection provides an overview of recent advances in detergent chemistry covering progress in synthesis, supramolecular characterization, and application. Our collection shows that detergent chemists operate usually interdisciplinary. Connecting molecular structures of detergents with properties relevant to applications is at the center of scientific exploitation. Detergent chemists deliver solutions to research and industry that aim at securing well‐being, hygiene, and new pharmaceuticals.

PEG detergents are important tools in the biophysical characterization of membrane protein whose utility is often limited by their intrinsic denaturing properties. This work addresses the question of whether changing the linker between PEG headgroup and nonpolar tail can modulate the denaturing properties of these detergents. To address this question, herein, we introduce the modular architecture of PEG550 detergents and explore its utility for protein purification from membranes and detergent exchange. Our results indicate that PEG550 detergents cannot efficiently solubilize proteins from lysed bacterial membranes. Varying the linker cannot eliminate the denaturing properties that PEG550 detergents can have on a protein during extraction and affinity purification. Interestingly, we find that PEG550 detergents can preserve the secondary structure and activity of the model membrane protein vitamin B12 transporter as good as the reference detergent n-dodecyl-β-D-maltoside following detergent exchange via drop dilution. Our findings clarify that denaturing properties of PEG550 detergents depend on both their chemical structure and the detergent exchange method with which proteins and detergents are brought together. Our drop dilution conditions are representative of those frequently employed in the biophysical characterization of membrane proteins. We anticipate PEG550 detergents will deliver a starting point for the optimization of sample properties in the biophysical characterization of membrane proteins.

Membrane protein complexes regulate many biological functions, yet they are incredibly challenging to handle. Detergents are a key enabling technology for purification and analysis as they can provide membrane proteins with controlled solubility, stability, and heterogeneity. However, the design criteria for detergents that enable both the purification and analysis of membrane proteins with their associated lipids remain unclear. Here, we leverage the modular nature of nonionic hybrid detergents to chemically tune molecular parameters that are important for maintaining native oligomeric states of membrane protein complexes and copurifying lipids. Tuning the hydrophilic‐lipophilic balance (HLB), and the relative size of a nonionic head in proximity to a tetraethylene glycol headgroup, led to altered charge reduction, retention of protein oligomers and changed the relative degree of copurifying lipids from purification to analysis in a predictable manner. Our findings represent a significant step forward in the investigation of membrane proteins and interactions with lipids.

Detergents are key reagents in bottom‐up proteomics that create an apparent, yet underappreciated bias on observable proteomes. Maximizing the chemical diversity of detergents in parallelized screens is supposed to maximize observable proteomes if proteomics data sets of different detergents are combined. The aim of our work is to investigate the potential of fusing ionic and nonionic detergent headgroups into hybrid detergents for increasing the observable number of unique protein identities. Our data indicate that the solubilizing properties of hybrid detergents do not reflect an average of canonical detergents. The number of unique protein identities obtainable from an Escherichia coli screen increases from 1604 to 2169 when proteomics data sets from sodium dodecyl sulfate, dodecyltrimethylammonium bromide, dendritic triglycerol detergent, and related hybrid detergents are combined. Our data highlight the utility of cationic detergents and related hybrid detergents for enhancing observable proteomes. Detergent screening–based proteome reconstructions with canonical detergents and hybrid detergents present an interesting research direction towards improved proteome profiling applications.

Non‐ionic detergents are key reagents for the characterization of membrane protein drug targets. Suitable detergents are commonly identified by trial and error, which leads to failed preparations and raising costs. Recent findings suggest that not only the chemistry of detergents but also the strategy with which detergents and proteins are brought together impact the successes of investigations. To facilitate the future development of non‐ionic detergents in membrane protein research, herein, we review chemical design concepts and detergent exchange strategies for a successful integration of detergents into the analysis of challenging membrane protein complexes. Our overview reveals exciting opportunities to tackle existing challenges, including the stabilization of G‐protein coupled receptors, the development of fluorinated detergents for studying protein–lipid binding, top‐down design of detergents, and hybrid detergents for the identification of non‐canonical lipid associations to proteins with relevance to antibiotic research. Our review will facilitate the development of chemical tools for the biophysical characterization of membrane proteins and support the discovery of biological findings in the future.