2.A.17.1.1
Di- or tripeptide:H⁺ symporter of 497 aas and 13 or 14 TMSs. DtpT is specific for di- and tripeptides, with the highest affinities for peptides with at least one hydrophobic residue. The effect of the hydrophobicity, size, or charge of the amino acid was different for the amino- and carboxyl-terminal positions of dipeptides. Free amino acids, omega-amino fatty acidss, and peptides with more than three amino acid residues do not interact with DtpT. For high-affinity interaction, the peptides need to have free amino and carboxyl termini, amino acids in the L configuration, and trans-peptide bonds. Comparison of the specificity of DtpT with those of the eukaryotic homologues PepT(1) and PepT(2) showed that the bacterial transporter is more restrictive in its substrate recognition. (Fang et al. 2000).