Proton-dependent permease that transports di- and tripeptides. Has a clear preference for dipeptides and tripeptides composed of L-amino acids, and discriminates dipeptides on the basis of the position of charges within the substrate. Inhibited by CCCP but unaffected by sodium depletion. Although DtpB appears to represent a system of lower affinity, there is an obvious redundancy in substrate specificity as compared with DtpA. Belongs to the major facilitator superfamily. Proton-dependent oligopeptide transporter (POT/PTR) (TC 2.A.17) family. DtpB subfamily.