Part of an ABC transporter complex involved in erythritol/L-threitol import. Binds erythritol and L-threitol. Functions in the transport for the degradation pathways of erythritol and L-threitol, that allow M.smegmatis to grow on these compounds as the sole carbon source. Up-regulated during growth on erythritol, D-threitol or L-threitol relative to growth on glycerol. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has not been experimentally proven. Cells lacking this gene are defective for growth on erythritol or on L-threitol. Belongs to the bacterial solute-binding protein 1 family.