Inhibition of Bacterial Sialic acid Transporters

The principle participants of the project, which funded by CARe and Vinnova (2018-2020; 6,69 MSEK), are: Rosmarie Friemann, CARe (Principle Investigator); Ulf Nilsson, Lund University; Ulf Ellervik, Lund University; and Red Glead Discovery.

Background
Many pathogenic and opportunistic bacteria have evolved the ability to scavenge and metabolise sialic acids1,2 – a large family of nine-carbon acidic monosaccharides prevalent in mucus rich environments3. In mammals, sialic acids are primarily found at the terminal end of cell surface glycoconjugates, where they mediate a diverse array of biological functions1,2,4,5. As such, bacteria that colonise sialylated environments deploy specific transporters to mediate import of scavenged sialic acids, including those from the ATP-binding cassette (ABC), tripartite ATP-independent periplasmic (TRAP), major facilitator superfamily (MFS) and sodium solute symporter (SSS) transporter families6,7. Once imported to the cytoplasm, bacteria utilise host-derived sialic acids either for molecular mimicry, where sialic acid is incorporated into their surface glycoconjugates, or use sialic acids as sources of carbon, nitrogen and energy1,8,9. Despite a growing understanding of the catalytic steps involved in cleavage of sialic acids from the host cell surface and subsequent cytoplasmic processing2,3, little is known about the molecular determinants of import. Disruption of the genes encoding sialic acid transporters impairs outgrowth of Salmonella enterica serovar Typhimurium and Clostridium difficile during post-antibiotic expansion10 and of Escherichia coli during intestinal inflammation11.

We have recently characterized and determined the first structure of a sialic acid transporter (SiaT) from Proteus mirabilis12. SiaT is a secondary active transporter of the SSS family, which use the Na+ electrochemical gradients as the driving force for the uptake of extracellular substrates. Homologs of SiaT are found in a wide range of pathogenic bacteria including Streptococcus pneumoniae, Salmonella enterica, Staphylococcus aureus and C. difficile.

We aim to characterize the structure–function relationships of sialic acid transporters and develop candidate inhibitors to demonstrate antimicrobial activities.

Based on the biophysical characterization and the SiaT structure, in silico methods have been used and the first round of compounds have been identified, chemically synthesized and evaluated using biophysical assays.
 

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