Molecular characterization of the interaction of sialic acid with the periplasmic binding protein from .

The primary role of bacterial periplasmic binding proteins is sequestration of essential metabolites present at a low concentration in the periplasm and making them available for active transporters that transfer these ligands into the bacterial cell. The periplasmic binding proteins (SiaPs) from the tripartite ATP-independent periplasmic (TRAP) transport system that transports mammalian host-derived sialic acids have been well studied from different pathogenic bacteria, including , , , and SiaPs bind the sialic acid -acetylneuraminic acid (Neu5Ac) with nanomolar affinity by forming electrostatic and hydrogen-bonding interactions. Here, we report the crystal structure of a periplasmic binding protein (SatA) of the ATP-binding cassette (ABC) transport system from the pathogenic bacterium The structure of -SatA in the native form and sialic acid-bound forms (with Neu5Ac and -glycolylneuraminic acid (Neu5Gc)), determined to 2.