Involved in the transport of alpha-galactosides. Required for the utilization of raffinose and melibiose. Probably acts as a periplasmic substrate-binding protein for a transport system. Induced by melibiose, raffinose, galactose, galactosamine, dulcitol and stachyose (PubMed:9791127, PubMed:17101990). Expression is down-regulated by succinate and glucose, and by SyrA (PubMed:9791127). Disruption mutant is unable to use melibiose and raffinose as carbon sources but it can use glucose and galactose. Belongs to the bacterial solute-binding protein 5 family.