Substrate-bound outward-open structure of a Na+-coupled sialic acid symporter reveals a new Na+ site

Many pathogenic bacteria utilise sialic acids as an energy source or use them as an external coating to evade immune detection. As such, bacteria that colonise sialylated environments deploy specific transporters to mediate import of scavenged sialic acids. Here, we report a substrate-bound 1.95 Å resolution structure and subsequent characterisation of SiaT, a sialic acid transporter from Proteus mirabilis. SiaT is a secondary active transporter of the sodium solute symporter (SSS) family, which use Na+ gradients to drive the uptake of extracellular substrates. SiaT adopts the LeuT-fold and is in an outward-open conformation in complex with the sialic acid N-acetylneuraminic acid and two Na+ ions. One Na+ binds to the conserved Na2 site, while the second Na+ binds to a new position, termed Na3, which is conserved in many SSS family members. Functional and molecular dynamics studies validate the substrate-binding site and demonstrate that both Na+ sites regulate N-acetylneuraminic acid transport

The binding mechanism of adhesin P subtype to globotetraosylceramide is associated with systemic disease

Streptococcus suis is part of the pig commensal microbiome but strains can also be pathogenic, causing pneumonia and meningitis in pigs as well as zoonotic meningitis. According to genomic analysis, S. suis is divided into asymptomatic carriage, respiratory and systemic strains with distinct genomic signatures. Since the strategies to target pathogenic S. suis are limited, new therapeutic approaches are needed. The virulence factor S. suis adhesin P (SadP) recognizes the galabiose Galα1-4Gal-oligosaccharide. Based on its oligosaccharide fine specificity, SadP can be divided into subtypes PN and PO We show here that subtype PN is distributed in the systemic strains causing meningitis, whereas type PO is found in asymptomatic carriage and respiratory strains. Both types of SadP are shown to predominantly bind to pig lung globotriaosylceramide (Gb3). However, SadP adhesin from systemic subtype PN strains also binds to globotetraosylceramide (Gb4). Mutagenesis studies of the galabiose-binding domain of type PN SadP adhesin showed that the amino acid asparagine-285, which is replaced by an aspartate residue in type PO SadP, was required for binding to Gb4 and, strikingly, was also required for interaction with the glycomimetic inhibitor phenylurea-galabiose. Molecular dynamics simulations provided insight into the role of Asn-285 for Gb4 and phenylurea-galabiose binding, suggesting additional hydrogen bonding to terminal GalNAc of Gb4 and urea-group. Thus, the Asn-285-mediated molecular mechanism of type PN SadP binding to Gb4 could be used to selectively target S. suis in systemic disease without interfering with commensal strains, opening up new avenues for interventional strategies against this pathogen.<br /

Substrate-bound outward-open structure of a Na+-coupled sialic acid symporter reveals a new Na+ site

© 2018 The Author(s). Many pathogenic bacteria utilise sialic acids as an energy source or use them as an external coating to evade immune detection. As such, bacteria that colonise sialylated environments deploy specific transporters to mediate import of scavenged sialic acids. Here, we report a substrate-bound 1.95 Å resolution structure and subsequent characterisation of SiaT, a sialic acid transporter from Proteus mirabilis. SiaT is a secondary active transporter of the sodium solute symporter (SSS) family, which use Na+gradients to drive the uptake of extracellular substrates. SiaT adopts the LeuT-fold and is in an outward-open conformation in complex with the sialic acid N-acetylneuraminic acid and two Na+ions. One Na+binds to the conserved Na2 site, while the second Na+binds to a new position, termed Na3, which is conserved in many SSS family members. Functional and molecular dynamics studies validate the substrate-binding site and demonstrate that both Na+sites regulate N-acetylneuraminic acid transport

Correction to: "Target inhibition of galectin-3 by inhaled TD139 in patients with idiopathic pulmonary fibrosis." Nikhil Hirani, Alison C. MacKinnon, Lisa Nicol, et al. <em>Eur Respir J</em> 2021; 57: 2002559

\ua9 2022 European Respiratory Society. All rights reserved. In the aforementioned research article published in the May 2021 issue of the European Respiratory Journal, the epithelial lining fluid (ELF) data used in figure 2c and d was calculated in error from an incorrect bronchoalveolar lavage (BAL) fluid data set. The incorrect data was from the resuspended BAL cell preparation rather than the true BAL fluid concentrations in the supernatant generated post-BAL cell centrifugation. The correct data from the BAL fluid supernatants following the removal of BAL cells has now been used to calculate the ELF data and this has been corrected in figure 2c and d. The caption to figure 2 has also been updated to reflect these changes. These corrections do not impact the interpretation of the data or the conclusions of the paper, and no other parts of the article have been affected by this correction.The new figure with the updated caption is below, and the article has been corrected and republished online