Part of an ABC transporter complex involved in D-threitol import. Binds D-threitol. Functions in the transport for the degradation pathway of D-threitol, that allows M.smegmatis to grow on this compound as the sole carbon source. Highly up-regulated during growth on D-threitol relative to growth on glycerol. Cells lacking this gene are defective for growth with D-threitol. Belongs to the bacterial solute-binding protein 2 family.