Proton-dependent permease that transports di- and tripeptides as well as structurally related peptidomimetics such as aminocephalosporins into the cell. 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. Monomer (Probable). Has a crown-like structure with a diameter of 8 nm and a central density. Transcriptionally activated by the EnvZ/OmpR regulatory system. Belongs to the major facilitator superfamily. Proton-dependent oligopeptide transporter (POT/PTR) (TC 2.A.17) family. DtpA subfamily.