Part of the ABC transporter complex GsiABCD involved in glutathione import (PubMed:16109926). Binds glutathione (PubMed:30515393). The complex is composed of two ATP-binding proteins (GsiA), two transmembrane proteins (GsiC and GsiD) and a solute-binding protein (GsiB) (Probable). In the presence of glutathione, interacts with the transmembrane proteins GsiC and GsiD (PubMed:30515393). Glutathione binding may promote conformational change, from inactive to active form. Belongs to the bacterial solute-binding protein 5 family.