Biology subjects

Jimah, J. R.

Publications and source records attributed to Jimah, J. R..

4 recordsLinked to original sources

bioRxiv2022

Conformational flexibility, lipid binding, and regulatory domains in CelTOS

CelTOS is an essential Plasmodium traversal protein and conserved in apicomplexan parasites. We showed that CelTOS forms pores in cell membranes to enable traversal of parasites through cells (Jimah et al., 2016). Here, we establish roles for the distinct regions of CelTOS, examine the mechanism of pore formation and evaluate the immunogenicity of engineered CelTOS variants. CelTOS dimer dissociation is required for pore formation as disulfide bridging between monomers inhibits pore formation and this inhibition is rescued by disulfide-bridge reduction. A helix destabilizing Pro127 allows CelTOS to undergo significant conformational changes to assemble into pores. The flexible C-terminus of CelTOS is a negative regulator that limits pore formation. Lipid binding is a pre-requisite for pore assembly as mutation of a phospholipid binding site in CelTOS resulted in loss of lipid binding and abrogated pore formation. The disulfide-locked and N-terminal deletion mutants showed improved immunogenicity relative to wild-type CelTOS in mice. These findings have implications for pore-forming proteins that are essential for diverse functions, identify critical regions in CelTOS, and will guide the design of effective CelTOS-targeting vaccines to combat infection and transmission of malaria and apicomplexan parasites.

microbiology↗

bioRxiv2021

Cryo-EM structures reveal multiple stages of bacterial outer membrane protein folding

Transmembrane {beta}-barrel proteins are folded into the outer membrane (OM) of Gram-negative bacteria by the {beta}-barrel assembly machine (BAM) via an unexplained process that occurs without known external energy sources. Here we used single-particle cryo-EM to visualize the folding dynamics of a model {beta}-barrel protein (EspP) by BAM. We found that BAM binds the highly conserved "{beta}-signal" motif of EspP to correctly orient {beta}-strands in the OM during folding. We also found that the folding of EspP proceeds via remarkable "hybrid-barrel" intermediates in which membrane integrated {beta}-sheets are attached to the essential BAM subunit, BamA. The structures show an unprecedented deflection of the membrane surrounding the EspP intermediates and suggest that {beta}-sheets progressively fold towards BamA to form a {beta}-barrel. Along with in vivo experiments that tracked {beta}-barrel folding while the OM tension was modified, our results support a model in which BAM harnesses OM elasticity to accelerate {beta}-barrel folding.

biochemistry↗

bioRxiv2020

The structure and spontaneous curvature of clathrin lattices at the plasma membrane.

Clathrin mediated endocytosis is the primary pathway for receptor and cargo internalization in eukaryotic cells. It is characterized by a polyhedral clathrin lattice that coats budding membranes. The mechanism and control of lattice assembly, curvature, and vesicle formation at the plasma membrane has been a matter of longstanding debate. Here, we use platinum replica and cryo electron microscopy and tomography to present a global structural framework of the pathway. We determine the shape and size parameters common to clathrin-mediated endocytosis. We show that clathrin sites maintain a constant surface area during curvature across multiple cell lines. Flat clathrin is present in all cells and spontaneously curves into coated pits without additional energy sources or recruited factors. Finally, we attribute curvature generation to loosely connected and pentagon-containing flat lattices that can rapidly curve when a flattening force is released. Together, these data present a new universal mechanistic model of clathrin-mediated endocytosis.

cell biology↗

bioRxiv2019

The mechanisms of dynamin-actin interaction

Cell-cell fusion is an indispensable process in the conception, development and physiology of multicellular organisms. Here we demonstrate a direct and noncanonical role for dynamin, best known as a fission GTPase in endocytosis, in cell-cell fusion. Our genetic and cell biological analyses show that dynamin colocalizes within the F-actin-enriched podosome-like structures at the fusogenic synapse, which is required for generating invasive membrane protrusions and myoblast fusion in vivo, in an endocytosis-independent manner. Biochemical, negative stain EM and cryo-electron tomography (cryo-ET) analyses revealed that dynamin forms helices that directly bundles actin filaments by capturing multiple actin filaments at their outer rim via interactions with dynamins proline-rich domain. GTP hydrolysis by dynamin triggers disassembly of the dynamin helix, exposes the sides of the actin filaments, promotes dynamic Arp2/3-mediated branched actin polymerization, and generates a mechanically stiff actin network. Thus, dynamin functions as a unique actin-bundling protein that enhances mechanical force generation by the F-actin network in a GTPase-dependent manner. Our findings have universal implications for understanding dynamin-actin interactions in various cellular processes beyond cell-cell fusion.

cell biology↗