Biology subjects

Lim, N. Z.-L.

Publications and source records attributed to Lim, N. Z.-L..

2 recordsLinked to original sources

bioRxiv2025

Lipid interactions are important for the Tol-Pal complex in maintaining outer membrane lipid homeostasis

Gram-negative bacteria are intrinsically resistant to many antibiotics in part due to the asymmetric architecture and barrier function of their outer membrane (OM). To establish proper lipid asymmetry, cells need to ensure an intricate balance of constituent OM components, especially lipids. In this regard, the conserved, trans-envelope Tol-Pal complex plays a primary role in maintaining OM lipid homeostasis, thus OM integrity, possibly via retrograde phospholipid transport. However, mechanistic details for this process are unknown, owing to the lack of evidence for direct lipid binding. In this study, we discover that the periplasmic protein TolB, a key component of the Tol-Pal system, associates directly with membranes in vitro, via specific interactions with cardiolipin (CL). Using coarse-grained molecular dynamics simulations, we identify a CL-binding site on TolB; a single amino acid mutation at this site abolishes in vitro membrane interaction, consequently impairing cellular Tol-Pal function in maintaining OM homeostasis in Escherichia coli. Curiously, we find that the functional requirement for TolB-CL interactions can be partially bypassed in cells lacking CL, suggesting compensatory effects through other lipids only when CL is absent. Our findings reveal a previously unappreciated lipid-binding role for TolB, and provide novel insights into how the Tol-Pal complex may facilitate phospholipid transport across the cell envelope. Our work will inform future strategies towards developing new antibiotics against Gram-negative bacteria.

biochemistry↗

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↗