Responsible for transport of beta-galactosides into the cell, with the concomitant import of a proton (symport system). Can transport lactose, melibiose, lactulose or the analog methyl-1-thio-beta,D-galactopyranoside (TMG), but not sucrose or fructose (PubMed:1848449, PubMed:18177889, PubMed:22106930). The substrate specificity is directed toward the galactopyranosyl moiety of the substrate (PubMed:22106930). Monomer. Belongs to the major facilitator superfamily. Oligosaccharide:H(+) symporter (OHS) (TC 2.A.1.5) family.