Biology subjects

Swart, A. L.

Publications and source records attributed to Swart, A. L..

3 recordsLinked to original sources

bioRxiv2026

The Legionella phosphocholinase AnkX modulates IMPDH2 regulation and cytoophidia dynamics

Legionella pneumophila, the causative agent of Legionnaires disease, secretes more than 300 different effector proteins into the host cell to modulate processes such as signal transduction, membrane dynamics, and metabolism. A key regulator of cellular metabolism and proliferation is inosine 5-monophosphate dehydrogenase type II (IMPDH2), which catalyzes the rate-limiting step of de novo GTP biosynthesis. IMPDH2 assembles into filaments and larger structures known as cytoophidia, which enable fine-tuned regulation of enzymatic activity in response to changing nucleotide demands. Here, we identify human IMPDH2 as a previously unrecognized host target of the Legionella effector AnkX. We show that AnkX post-translationally modifies IMPDH2 within its regulatory domain by covalently attaching a phosphocholine moiety. While this post-translational modification does not alter the catalytic activity of IMPDH2, it disrupts filament formation, thereby impairing nucleotide-dependent regulation of enzyme activity. Consequently, AnkX-mediated phosphocholination affects IMPDH2 filament assembly, cytoophidia formation, and subcellular localization to the specific Legionella-containing vacuole (LCV). Thus, L. pneumophila subverts host GTP metabolism by posttranslationally modifying a central enzyme of the GTP biosynthetic pathway. Graphical abstract description O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=170 SRC="FIGDIR/small/701698v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@18f7724org.highwire.dtl.DTLVardef@1d70e86org.highwire.dtl.DTLVardef@1fa8890org.highwire.dtl.DTLVardef@11bc5ba_HPS_FORMAT_FIGEXP M_FIG C_FIG The Legionella effector AnkX post-translationally modifies the human host enzyme IMPDH2 by transferring a phosphocholine group using CDP-choline as co-substrate. We identified the modification site and discovered that this post-translational modification disrupts the ability of IMPDH2 to assemble into filaments and cytoophidia. By shifting the equilibrium toward free octamers, AnkX-mediated PCylation perturbs the structural regulation of IMPDH2 and alters GTP metabolism in L. pneumophila-infected host cells. This figure was inspired by (https://www.biorxiv.org/content/10.1101/2024.07.29.605679v2).

microbiology↗

bioRxiv2025

The Legionella effector RidL promotes mitochondrial fragmentation through phosphorylation activation of the large GTPase Drp1

Intracellular pathogens such as Legionella pneumophila secrete effector proteins that manipulate host cell processes to promote bacterial survival. One such effector, RidL, is known to inhibit retrograde trafficking by interacting with the retromer complex via its N-terminal domain. Here, we identify a second function of RidL mediated by its C-terminal domain, which directly binds to the mitochondrial fission GTPase Drp1 and related large GTPases. In vitro, RidL reduces Drp1 GTPase activity and disrupts its oligomerization. During infection, RidL localizes to mitochondria, enhances the accumulation of Drp1 and the outer membrane protein Tom20, and impairs mitochondrial dynamics and function. Moreover, in L. pneumophila-infected cells, RidL promotes phosphorylation of Drp1 at Ser616, leading to Drp1 activation and mitochondrial fragmentation. These findings establish RidL as a bifunctional effector that targets both the retromer complex and Drp1 through distinct domains. By interfering with host mitochondrial dynamics, RidL enables L. pneumophila to remodel host organelles and optimize conditions for intracellular replication.

microbiology↗

bioRxiv2023

Goblet cell invasion promotes breaching of respiratory epithelia by an opportunistic human pathogen

While commensal bacteria generally respect natural barriers of the human body, pathogens are able to breach epithelia, invade deeper tissue layers and cause life-threatening infections. Pseudomonas aeruginosa, an opportunistic human pathogen, is a leading cause of severe hospital-acquired pneumonia, with mortality rates as high as 50% in mechanically ventilated patients1-3. Effective colonization and breaching of lung mucosa are hallmarks of P. aeruginosa pathogenesis4. Although virulence factors and behavioral strategies of P. aeruginosa have been described5,6, it has remained unclear how this pathogen disseminates on functional mucosal surfaces, how it avoids mucociliary clearance and how it invades the tissue barrier. Using fully differentiated human lung epithelia, we demonstrate that P. aeruginosa efficiently spreads on the apical tissue surface before it breaches epithelia by specifically invading mucus secreting goblet cells. Internalization leads to host cell death and expulsion and the formation of ruptures of the epithelial barrier. Rupture sites are rapidly colonized by extracellular bacteria through active chemotaxis, leading to increasing tissue damage and successful pathogen translocation to the unprotected basolateral side of the epithelium. We show that cell invasion is promoted by two Type-6 toxin secretion systems (T6SS), while Type-3 (T3SS) mediates cell death of infected goblet cells. T3SS mutants invade goblet cells normally, but internalized bacteria fail to trigger goblet cell expulsion and instead show unrestrained intracellular replication. While the effective shedding of infected host cells reveals potent tissue protection mechanisms, the discovery of an intracellular lifestyle of P. aeruginosa in human lung epithelia provides new entry points into investigating the intersection of antibiotic and immune mechanisms during lung infections. By demonstrating that P. aeruginosa uses a combination of specific virulence factors and collective behavior to invade goblet cells and breach the lung tissue barrier from within, these studies reveal novel mechanisms underlying lung infection dynamics under physiological conditions.

microbiology↗