Biology subjects

Yeow, J.

Publications and source records attributed to Yeow, J..

8 recordsLinked to original sources

bioRxiv2026

A recipient-based anti-conjugation factor triggers an abortive mechanism by targeting the Type IV secretion system

Many bacterial defense (immune) systems prevent the entry of foreign DNA by directly recognizing and targeting nucleic acids, effectively blocking all mechanisms of horizontal gene transfer1. However, systems defending specifically against conjugation, a major route for gene dissemination, have heretofore not been reported. We have discovered a novel defense factor, which we name AbjA (Abortive conjugation protein A), that specifically limits successful plasmid conjugation into a recipient bacterium. AbjA interacts directly with and targets the ATPase component TrbE of the Type IV secretion system (T4SS)2,3 to induce cell death; this contrasts with most other defense systems that act at the nucleic acid level. AbjA therefore represents the first member of a new class of bacterial defense factors that trigger what we term abortive conjugation. Previously, recipient bacteria were viewed largely as defenseless against the mechanism of conjugation4-6; our discovery and characterization of AbjA demonstrates that recipient bacteria can block conjugation to limit the transfer (and thus spread) of plasmids. Discovery of this class of defense systems thus has implications for bacterial defense, plasmid evolution, and possible strategic alternatives to rationally target plasmid spread, particularly with respect to virulence and antibiotic resistance.

microbiology↗

bioRxiv2026

An injectable soft implant for long-acting, reversible, ultra-stable release of therapeutics

Providing long-term (>6 months) zero-order drug release from easily administered formulations is a key challenge in improving patient adherence and facilitating access. Herein, we report the design and development of an injectable, biodegradable, long-acting polymeric microparticle-embedded hydrogel platform for prolonged, zero-order release of therapeutics. This "soft implant" is injectable for ease of administration and can be retrieved via a small incision, allowing for discontinuation of therapy if desired. Central to the platform are surface-eroding poly(orthoester) (POE) microparticles, which were molecularly tailored to tune zero-order drug release across a wide range of timeframes. We demonstrate the clinical potential of the "soft implant" using levonorgestrel, a contraceptive agent requiring sustained dosing. In vitro, we observed zero-order release for 300 days, projected for >12 months, with behavior consistent with surface erosion further supported through Raman chemical mapping. In vivo studies confirmed zero-order release for six months, projected to 12 months, from a subcutaneous injection in rats. We envision that our platform could transform therapies that require long-term, regular drug dosing, significantly improving compliance and therapy outcomes.

bioengineering↗

bioRxiv2025

Polar localization of putative phospholipid transporters in Escherichia coli

The Gram-negative bacterial cell envelope comprises an outer membrane (OM) with an asymmetric arrangement of lipopolysaccharides (LPS) and phospholipids (PLs), protecting them from both physical and chemical threats. To build the OM, PLs must be transported across the cell envelope; this process has remained elusive until recently, where three collectively essential AsmA-superfamily proteins - YhdP, TamB, and YdbH - are proposed to function as anterograde PL transporters in Escherichia coli. Here, we identify the cell wall-binding protein DedD as a novel interacting partner of YhdP, and discover that all three AsmA-superfamily proteins are recruited to, and strongly enriched at the cell poles. Our observation raises the possibility that anterograde PL transport could be spatially restricted to the cell poles, and highlights the importance of understanding the spatial-temporal regulation of OM biogenesis in coordination with cell growth and division.

microbiology↗

bioRxiv2024

Structural insights into the force-transducing mechanism of a motor-stator complex important for bacterial outer membrane lipid homeostasis

Gram-negative bacteria assemble an asymmetric outer membrane (OM) that functions as an effective barrier against antibiotics. Building a stable and functional OM requires assembly and maintenance of balanced levels of proteins, lipopolysaccharides, and phospholipids into the bilayer. In Escherichia coli, the trans-envelope Tol-Pal complex has recently been established to play a primary role in maintaining OM lipid homeostasis. It is believed that the motor-stator complex TolQR exploits the proton motive force in the inner membrane to induce conformational changes in the TolA effector, ultimately generating a force across the cell envelope to activate processes at the OM. Molecular details of how such force transduction occurs via the TolQRA complex is unknown. Here, we solve structures of the E. coli TolQRA complex using single particle cryo-EM, capturing the transmembrane (TM) regions of the purified complex in two distinct states at [~]3.6 [A] and [~]4.2 [A] nominal resolutions. We define how the TolA N-terminal TM helix interacts with an asymmetric TolQ5R2 sub-complex in two different positions, revealing how the two TolQRA states are related by rotation of the TolQ pentamer. By considering structural prediction of the periplasmic domains of the complex, we propose a working model for how proton passage through the complex induces rotary movement that can be coupled to TolA for force transduction across the cell envelope.

biophysics↗

bioRxiv2024

Nanoscale biodegradable printing for designed tuneability of vaccine delivery kinetics

Two photon polymerization (2PP) 3D printing enables top-down biomaterial synthesis with nanoscale spatial resolution for de novo design of monodisperse injectable drug delivery systems. To address the limitations of current 2PP resins, we developed Spatiotemporal Controlled Release Inks of Biocompatible polyEsters (SCRIBE), a novel poly(lactic-co-glycolic acid)-triacrylate resin family with sub-micron resolution and tuneable hydrolysis. SCRIBE enables direct printing of hollow microparticles with tuneable chemistry and complex geometries inaccessible to molding techniques, which we use to engineer controlled protein release in vitro and in vivo. We use SCRIBE microparticles to modulate antibody titers and class switching as a function of antigen release rate and extend these findings to enable a single-injection vaccine formulation with extended antibody induction kinetics. Demonstrating how the chemistry and CAD of 2PP-printed microparticles can be used to tune responses to biomacromolecule release in vivo opens significant opportunities for a new generation of drug delivery vehicles. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=117 SRC="FIGDIR/small/616252v1_ufig1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@a2e8c0org.highwire.dtl.DTLVardef@15ecbf1org.highwire.dtl.DTLVardef@9f734forg.highwire.dtl.DTLVardef@4b7e39_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2024

The level of endothelial glycocalyx maturity modulates interactions with charged nano-materials

Nanomaterials have been extensively investigated for their potential in delivering therapeutics to target tissues, but few have advanced to clinical application. The luminal surface of endothelial cells that line blood vessels are covered by a glycocalyx, a complex extracellular matrix rich in anionic glycans. However, the role of this glycocalyx in governing nanomaterial-cell interactions is often overlooked. In this study, we demonstrate that gold nanoparticles functionalized with branched polyethyleneimine (AuNP+) bind to primary human endothelial cells expressing either a developing or mature glycocalyx, with the interaction involving hyaluronan and heparan sulfate. Notably, the mature glycocalyx decreases the toxicity of AuNP+. In contrast, lipoic acid-functionalized gold nanoparticles (AuNP-) bind to endothelial cells with a developing glycocalyx, but not a mature glycocalyx. To further investigate this phenomenon, we studied charged polymers, including poly(arginine) (polyR) and poly(glutamic acid) (polyE). PolyE does not associate with endothelial cells regardless of glycocalyx maturity, but when glycans are enzymatically degraded, it can bind to the cells. Conversely, polyR associates with endothelial cells irrespective of glycocalyx maturity or glycan degradation. These findings highlight the intricate relationship between nanomaterial charge and presentation in interactions with endothelial cells, offering insights for modulating nanomaterial interactions with the blood vessel wall.

bioengineering↗

bioRxiv2022

Conformational changes induced by chaperone interactions facilitate lipid transport critical for bacterial outer membrane asymmetry

The outer membrane (OM) of Gram-negative bacteria is an asymmetric lipid bilayer with outer leaflet lipopolysaccharides (LPS) exposed to extracellular milieu and inner leaflet phospholipids (PLs) facing the periplasm. This unique lipid asymmetry is the key to its innate drug resistance, rendering the OM impermeable to external insults, including antibiotics and bile salts. To maintain this OM barrier, the OmpC-Mla system removes mislocalized PLs from the OM outer leaflet, and transports them back to the inner membrane (IM); in the first step, the OM OmpC-MlaA complex transfers PLs to the periplasmic chaperone MlaC. This process likely occurs via a hydrophilic channel in MlaA, yet mechanistic details have remained elusive. Here, we biochemically and structurally characterize the architecture of the MlaA-MlaC transient complex. We map the interaction surfaces between MlaA and MlaC in Escherichia coli, revealing that MlaC binds MlaA at the periplasmic face in a manner that possibly juxtaposes the MlaA channel and the MlaC lipid binding cavity. In addition, we show that electrostatic interactions between the putative C-terminal tail helix of MlaA and a surface patch on MlaC are important for recruitment of the latter to the OM. We further provide biochemical evidence for conformational changes in the MlaA channel that correlate with interactions with MlaC and OM porins, as well as functional states of MlaA. Finally, we solve a 2.9-[A] cryo-EM structure of OmpC-MlaA in nanodiscs in a disulfide-trapped complex with MlaC, reinforcing the mechanism of MlaC recruitment, and highlighting membrane thinning as a plausible strategy for directing lipids into the MlaA channel. Our work offers critical insights into how the OmpC-MlaA complex catalyzes retrograde transport of PLs to the IM to maintain OM lipid asymmetry.

biochemistry↗

bioRxiv2017

Molecular basis for the maintenance of lipid asymmetry in the outer membrane of Escherichia coli

A distinctive feature of the Gram-negative bacterial cell envelope is the asymmetric outer membrane (OM), where lipopolysaccharides (LPS) and phospholipids (PLs) reside in the outer and inner leaflets, respectively. This unique lipid asymmetry renders the OM impermeable to external insults. In Escherichia coli, the OmpC-MlaA complex is believed to maintain lipid asymmetry by removing mislocalized PLs from the outer leaflet of the OM. How it performs this function is unknown. Here, we define the molecular architecture of the OmpC-MlaA complex to gain insights into its role in PL transport. We establish that MlaA sits entirely within the bilayer in complex with OmpC and provides a hydrophilic channel possibly for PL translocation across the OM. Furthermore, we show that flexibility in a hairpin loop adjacent to the channel modulates MlaA activity. Finally, we demonstrate that OmpC plays an active role in maintaining OM lipid asymmetry together with MlaA. Our work offers glimpses into how the OmpC-MlaA complex transports PLs across the OM and has important implications for future antimicrobial drug development.

biochemistry↗