Biology subjects

Baumann, C. G.

Publications and source records attributed to Baumann, C. G..

6 recordsLinked to original sources

bioRxiv2025

Persistent LPS insertion, spatial segregation and vesicle biogenesis drive growth-independent adaptation of the Escherichia coli outer membrane

The barrier and load-bearing functions of the Gram-negative bacterial outer membrane (OM) depend on ordered, dense packing of lipopolysaccharide (LPS), the major constituent of its outer leaflet. Despite its importance, LPS spatiotemporal dynamics and turnover mechanisms remain poorly understood. Existing models posit that LPS turnover only occurs via passive dilution during growth-dependent OM expansion, restricting adaptive LPS turnover, especially in nutrient-limited conditions. Here, using innovative pulse-chase LPS metabolic labelling techniques in combination with super-resolution microscopy, we demonstrate that Escherichia coli maintains OM homeostasis through continuous removal of pre-existing LPS and insertion of new LPS, even during stationary phase. We show that newly inserted LPS localises at discrete sites across the OM, remaining spatially segregated from pre-existing, background LPS. These observations challenge established OM organisational principles, suggesting an insertion-trapping mechanism can maintain LPS-rich clusters independent of a thermodynamically-driven phase separation. Time-lapse super-resolution imaging, biochemical assays, and nanoparticle tracking collectively reveal that OM vesicle (OMV) release mediates background LPS clearance. Our findings reveal bacteria have the capacity to remodel their surface architecture through OMV-mediated LPS turnover in a growth- independent manner. These insights redefine OM homeostasis and establish OMV biogenesis as fundamental to OM adaptation in Gram-negative bacteria.

microbiology↗

bioRxiv2025

The role of Akkermansia muciniphila sulfatases in colonic mucinutilisation

Akkermansia muciniphila, an obligate mucin degrader, is a major member of the human colonic microbiota and has been associated positive health outcomes. Mucins are complex glycoproteins that contain heavily sulfated O-glycans and form the protective colonic mucus layer. Bacterial carbohydrate sulfatases are required to metabolise these heavily sulfated mucin glycans and excessive bacterial foraging has been associated with several diseases. Sulfatases have been linked with inflammatory bowel disease, making these microbiota enzymes potential drug targets. A. muciniphila expresses carbohydrate sulfatases that can act on colonic mucins yet their roles in its metabolism remain opaque. Our data reveal that A. muciniphila requires glycopeptides/protein forms of colonic mucin for metabolism and its sulfatases have unique adaptations compared to Bacteroides species. Localisation studies reveal that desulfation of N-acetyl-D-glucosamine, but not D-galactose, is exclusively periplasmic. A cell surface sulfatase has a novel carbohydrate binding module that binds to colonic mucin. This paints a contrasting picture of sulfated mucin metabolism by Akkermansia muciniphila versus Bacteroides species. These data will be important for understanding the contexts for Akkermansia muciniphilas positive health correlations.

biochemistry↗

bioRxiv2025

Lipopolysaccharide lateral mobility in the Gram-negative bacterial outer membrane is confined and governed by interactions within the conserved Lipid A anchor

The Gram-negative bacterial cell envelope is defined by an asymmetric outer membrane where the outer leaflet adopts a highly ordered structure composed principally of lipopolysaccharide molecules. The organisation and dynamics of these glycolipids are key to the ability of the outer membrane to act as an innate barrier against chemical and antibiotic challenges, and as a load bearing element for the cell. Strong intermolecular forces are thought to govern the lateral diffusion of lipopolysaccharide in the outer membrane, but the extent and molecular basis of this diffusion has remained a controversial topic for over 50 years. Here we use a bio-orthogonal labelling strategy and in vivo fluorescence microscopy to unequivocally demonstrate extreme lateral confinement of lipopolysaccharide in the outer membrane of Escherichia coli, regardless of carbohydrate domain size and structure. We specifically identify magnesium cation-mediated interactions at the base of the carbohydrate and hydrophobic interactions within the lipid milieu as critical for lipopolysaccharide confinement. Importantly, these traits are conserved across multiple pathogenic species irrespective of O-antigen and capsular serotype. Together, these findings establish lipopolysaccharide endotoxin lateral confinement as a ubiquitous feature of the outer membrane and highlight potential universal vulnerabilities of the bacterial cell envelope.

microbiology↗

bioRxiv2022

Structural basis of DNA packaging by a ring-type ATPase from an archetypal viral system

Many essential cellular processes rely on substrate rotation or translocation by a multi-subunit, ring-type NTPase. A large number of double-stranded DNA viruses, including tailed bacteriophages and herpes viruses, use a homomeric ring ATPase to processively translocate viral genomic DNA into procapsids during assembly. Our current understanding of viral DNA packaging comes from three archetypal bacteriophage systems: cos, pac and phi29. Detailed mechanistic understanding exists for pac and phi29, but not for cos. Here we reconstituted in vitro a cos packaging system based on bacteriophage HK97 and provided a detailed biochemical and structural description. We used a photobleaching-based, single-molecule assay to determine the stoichiometry of the DNA-translocating ATPase large terminase. Crystal structures of the large terminase and DNA-recruiting small terminase, a first for both this phage and a cos system, reveal unexpected mechanistic similarities between cos and pac systems. At the same time, mutational and biochemical analyses indicate a new regulatory mechanism for ATPase multimerization and coordination in the HK97 system. This work therefore establishes a framework for studying the evolutionary relationships between ATP-dependent DNA translocation machineries in double-stranded DNA viruses.

biochemistry↗

bioRxiv2021

Subcellular dynamics and functional activity of the cleaved Na+ channel β1 subunit intracellular domain

The voltage-gated Na+ channel {beta}1 subunit, encoded by SCN1B, regulates cell surface expression and gating of subunits, and participates in cell adhesion. {beta}1 is cleaved by /{beta} and {gamma}-secretases, releasing an extracellular domain and intracellular domain (ICD) respectively. Abnormal SCN1B expression/function is linked to pathologies including epilepsy, cardiac arrhythmia, and cancer. In this study, we sought to determine the effect of secretase cleavage on {beta}1 function in breast cancer cells. Using a series of GFP-tagged {beta}1 constructs, we show that {beta}1-GFP is mainly retained intracellularly, particularly in the endoplasmic reticulum and endolysosomal pathway, and accumulates in the nucleus. Reduction in endosomal {beta}1-GFP levels occurred following {gamma}-secretase inhibition, implicating endosomes, and/or the preceding plasma membrane, as important sites for secretase processing. Using live-cell imaging, we report {beta}1ICD-GFP accumulation in the nucleus. Furthermore, {beta}1-GFP and {beta}1ICD-GFP both increased Na+ current, whereas {beta}1STOP-GFP, which lacks the ICD, did not, thus highlighting that the {beta}1-ICD was necessary and sufficient to increase Na+ current measured at the plasma membrane. Importantly, although the endogenous Na+ current expressed in MDA-MB-231 cells is TTX-resistant (carried by Nav1.5), the Na+ current increased by {beta}1-GFP or {beta}1ICD-GFP was TTX-sensitive. In addition, {beta}1-GFP increased mRNA levels of the TTX-sensitive subunits SCN1A/Nav1.1 and SCN9A/Nav1.7. Taken together, this work suggests that the {beta}1-ICD is a critical regulator of subunit function in cancer cells. Our data further highlight that {gamma}-secretase may play a key role in regulating {beta}1 function in breast cancer.

cell biology↗

bioRxiv2020

Periscope Proteins are variable length regulators of bacterial cell surface interactions

Changes at the cell surface enable bacteria to survive in dynamic environments, such as diverse niches of the human host. Here, we reveal "Periscope Proteins" as a widespread mechanism of bacterial surface alteration mediated through protein length variation. Tandem arrays of highly similar folded domains can form an elongated rod-like structure; thus variation in the number of domains determines how far an N-terminal host ligand binding domain projects from the cell surface. Supported by newly-available long-read genome sequencing data, we propose this new class could contain over 50 distinct proteins, including those implicated in host colonisation and biofilm formation by human pathogens. In large multi-domain proteins, sequence divergence between adjacent domains appears to reduce inter-domain misfolding. Periscope Proteins break this "rule", suggesting their length variability plays an important role in regulating bacterial interactions with host surfaces, other bacteria and the immune system.

microbiology↗