文摘
The uptake of exogenous solutes by prokaryotes is mediated by transport systems embedded in the plasma membrane. In many cases, a solute-binding protein (SBP) is utilized to bind ligands with high affinity and deliver them to the membrane-bound components responsible for translocation into the cytoplasm. In the present study, Avi_5305, an Agrobacterium vitis SBP belonging to Pfam13407, was screened by differential scanning fluorimetry (DSF) and found to be stabilized by an class="smallCaps">dan>-glucosamine and an class="smallCaps">dan>-galactosamine. Avi_5305 is the first protein from Pfam13407 shown to be specific for amino sugars, and co-crystallization resulted in structures of Avi_5305 bound to an class="smallCaps">dan>-glucosamine and an class="smallCaps">dan>-galactosamine. Typical of Pfam13407, Avi_5305 consists of two α/β domains linked through a hinge region, with the ligand-binding site located in a cleft between the two domains. Comparisons with Escherichia coli ribose-binding protein suggest that a cation–π interaction with Tyr168 provides the specificity for an class="smallCaps">dan>-glucosamine/an class="smallCaps">dan>-galactosamine over an class="smallCaps">dan>-glucose/an class="smallCaps">dan>-galactose.