The Sodium Sialic Acid Symporter From Staphylococcus aureus Has Altered Substrate Specificity

• Published in: Frontiers in chemistry 2018, Vol.6, p.233-233
• Main Authors: North, Rachel A, Wahlgren, Weixiao Y, Remus, Daniela M, Scalise, Mariafrancesca, Kessans, Sarah A, Dunevall, Elin, Claesson, Elin, Soares da Costa, Tatiana P, Perugini, Matthew A, Ramaswamy, S, Allison, Jane R, Indiveri, Cesare, Friemann, Rosmarie, Dobson, Renwick C J
• Format: Article
• Language: English
• Subjects: antibiotic resistance; Biochemistry and Molecular Biology; Biofysik; Biokemi och molekylärbiologi; Biophysics; Chemistry; Microbiology in the medical area; Mikrobiologi inom det medicinska området; sialic acids; SiaT; sodium solute symporter; Staphylococcus aureus
• ISSN: 2296-2646; 2296-2646
• DOI: 10.3389/fchem.2018.00233

Mammalian cell surfaces are decorated with complex glycoconjugates that terminate with negatively charged sialic acids. Commensal and pathogenic bacteria can use host-derived sialic acids for a competitive advantage, but require a functional sialic acid transporter to import the sugar into the cell. This work investigates the sodium sialic acid symporter (SiaT) from ( SiaT). We demonstrate that SiaT rescues an strain lacking its endogenous sialic acid transporter when grown on the sialic acids -acetylneuraminic acid (Neu5Ac) or -glycolylneuraminic acid (Neu5Gc). We then develop an expression, purification and detergent solubilization system for SiaT and demonstrate that the protein is largely monodisperse in solution with a stable monomeric oligomeric state. Binding studies reveal that SiaT has a higher affinity for Neu5Gc over Neu5Ac, which was unexpected and is not seen in another SiaT homolog. We develop a homology model and use comparative sequence analyses to identify substitutions in the substrate-binding site of SiaT that may explain the altered specificity. SiaT is shown to be electrogenic, and transport is dependent upon more than one Na ion for every sialic acid molecule. A functional sialic acid transporter is essential for the uptake and utilization of sialic acid in a range of pathogenic bacteria, and developing new inhibitors that target these transporters is a valid mechanism for inhibiting bacterial growth. By demonstrating a route to functional recombinant SiaT, and developing the and assay systems, our work underpins the design of inhibitors to this transporter.