Part of the ABC transporter complex GluABCD involved in glutamate uptake (PubMed:7868586). Binds glutamate with a high affinity (PubMed:32593757). Also binds aspartate with high affinity, suggesting that GluB could be involved in the transport of both amino acid residues into the cell (PubMed:32593757). Binding of glutamate or asparatate induces a higher thermal stability of the protein structure. The complex is composed of two ATP-binding proteins (GluA), two transmembrane proteins (GluC and GluD) and a solute-binding protein (GluB). Deletion of the gluABCD cluster almost abolishes glutamate uptake activity. Belongs to the bacterial solute-binding protein 3 family.