Biology subjects

Elantak, L.

Publications and source records attributed to Elantak, L..

3 recordsLinked to original sources

bioRxiv2026

A short C-terminal plug motif in a conserved type 4 pilus component controls pilus-tip localisation and filament biogenesis

Type 4a pili (T4aP), the most widespread and functionally versatile subtype of the type 4 filaments (T4F) superfamily, are functionalised at their tip by the adhesin PilC/PilY1. How this unusually large non-pilin protein is stably displayed at the pilus tip, and why is it required for pilus biogenesis, remains unknown. Here, using a multidisciplinary approach in Neisseria meningitidis, we show that the last 12 residues of PilC, representing ~1% of the protein, are both necessary and sufficient for pilus-tip localisation and filament biogenesis. X-ray crystallography reveals that this short "plug" motif binds the PilK subunit (within a complex of four minor pilins that caps the pilus) through {beta}-strand augmentation, a mode of interaction not previously characterised in T4F. Binding assays with synthetic peptides establish the specificity and affinity of this interaction, while the addition of a plug peptide extracellularly to cultures of a{Delta} pilC mutant restores pilus biogenesis. We show, using different methods, that the plug motif markedly stabilises PilK, providing an explanation for the requirement of PilC in pilus biogenesis. Consequently, expression of a PilK protein carrying a fused plug in N. meningitidis bypasses the requirement for PilC in pilus biogenesis. Together, these findings define the molecular basis of PilC/PilY1 function and localisation, reconcile all previous observations, and establish a broadly applicable model for T4aP biogenesis.

microbiology↗

bioRxiv2025

Atypical thioredoxin Patrx2 enhances alginate production in mucoid Pseudomonas aeruginosa

Pseudomonas aeruginosa, an opportunistic human pathogen, is known for its ability to respond and adapt to its environment, employing intricate adaptation mechanisms that can lead to the formation of complex biofilms. Redox processes play a pivotal role in bacterial adaptation mechanisms. The cytoplasm of most organisms is recognized for maintaining a reducing environment through thiol-disulfide oxidoreductases. In Pseudomonas aeruginosa, we have identified an unusual cytoplasmic thioredoxin named Patrx2. What sets Patrx2 apart is its active site, which contains a consensus sequence, CGHC, identical to the characteristic motif of protein disulfide isomerases (PDIs) found in eukaryotic cells. Our investigations have unveiled that Patrx2, unlike canonical thioredoxins, exhibits disulfide isomerase activity in vitro and displays physicochemical properties, as well as a structural conformation of its catalytic site, reminiscent of PDIs. Using a mutant transposon library, we found that the expression of patrx2 is regulated by the alternative sigma factor AlgU, which plays a crucial role in the formation of alginate biofilms in P. aeruginosa. We further demonstrated strong patrx2 expression in a mucoid strain we constructed, carrying the clinically relevant mucA22 mutation frequently found in cystic fibrosis patients. Furthermore, our results showed a significant decrease in alginate synthesis in a patrx2 mutant in this mucoid strain, which we attributed to its catalytic activity in a C34S variant. The study of Patrx2, an atypical thioredoxin expressed within an alginate biofilm, underscores the importance of redox regulation in adaptation mechanisms. Patrx2s involvement in alginate biosynthesis opens new pathway for inhibiting biofilm synthesis. HighlightsO_LIThe patrx2 gene is regulated by the alternative sigma factor AlgU C_LIO_LIPatrx2 is strongly produced in mucoid P. aeruginosa C_LIO_LIPatrx2 is an atypical thioredoxin with disulfide isomerase activity C_LIO_LIPatrx2 impacts alginate production in the mucoid P. aeruginosa mucA22 strain, likely through redox regulation of alginate biosynthesis. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=128 SRC="FIGDIR/small/667166v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@14f304forg.highwire.dtl.DTLVardef@1ecc15eorg.highwire.dtl.DTLVardef@8b18d9org.highwire.dtl.DTLVardef@c71b7_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2022

Pre-B cell receptor acts as a selectivity switch for Galectin-1 at the pre-B cell surface

Galectins are glycan binding proteins translating the sugar-encoded information of cellular glycoconjugates into many physiological activities including immunity, cell migration, and signaling. During early B lymphocytes (BL) development at the pre-B cell stage, BL express the pre-B cell receptor (pre-BCR) and are supported by mesenchymal stromal cells secreting Galectin-1 (Gal-1). Gal-1 interacts with glycosylated receptors from stromal and pre-B cell surfaces but also with the pre-BCR through a direct carbohydrate-independent contact. How this interaction might interplay with the glycan-decoding function of Gal-1 is unknown. Here, we investigated Gal-1 binding to cell surface ligands using NMR spectroscopy on native membranes. We showed that pre-BCR regulates Gal-1 binding to specifically target 2,3-sialylated receptors on pre-B cells. Upon pre-BCR interaction, dynamic changes resulted in additional contacts with 2,3-sialylated glycans converting Gal-1 from an exo- to an endo-type lectin. Remarkably, this selectivity switch is able to promote pre-B cell survival. Altogether, we shed light on a new mechanism allowing fine-tuning of Galectin specificity at the cell surfaces.

biochemistry↗