Part of the ABC transporter complex MelEDC-MsmX involved in melibiose, raffinose and stachyose import. Binds melibiose, raffinose and stachyose. The complex is composed of two ATP-binding proteins (MsmX), two transmembrane proteins (MelC and MelD) and a solute-binding protein (MelE). Repressed by the transcriptional regulator MelR. Induced by melibiose and raffinose. Deletion of the gene abolishes induction in the presence of melibiose and raffinose. Belongs to the bacterial solute-binding protein 1 family.