Peptide transporter isoforms are discriminated by the fluorophore‐conjugated dipeptides β‐Ala‐ and d ‐Ala‐Lys‐N‐7‐amino‐4‐methylcoumarin‐3‐acetic acid

Peptide transporters of the SLC 15 family are classified by structure and function into PEPT 1 (low‐affinity/high‐capacity) and PEPT 2 (high‐affinity/low‐capacity) isoforms. Despite the differences in kinetics, both transporter isoforms are reckoned to transport essentially all possible di‐ and tripeptides. We here report that the fluorophore‐conjugated dipeptide derivatives β ‐Ala‐Lys‐N‐7‐amino‐4‐methylcoumarin‐3‐acetic acid ( β ‐ AK ‐ AMCA ) and d ‐Ala‐Lys‐N‐7‐amino‐4‐methylcoumarin‐3‐acetic acid ( d ‐ AK ‐ AMCA ) are transported by distinct PEPT isoforms in a species‐specific manner. Transport of the fluorophore peptides was studied (1) in vitro after heterologous expression in X enopus oocytes of PEPT 1 and PEPT 2 isoforms from different vertebrate species and of PEPT 1 and PEPT 2 transporters from C aenorhabditis elegans by using electrophysiological and fluorescence methods and (2) in vivo in C . elegans by using fluorescence methods. Our results indicate that both substrates are transported by the vertebrate “renal‐type” and the C . elegans “intestinal‐type” peptide transporter only. A systematic analysis among species finds four predicted amino acid residues along the sequence that may account for the substrate uptake differences observed between the vertebrate PEPT 1/nematode PEPT 2 and the vertebrate PEPT 2/nematode PEPT 1 subtype. This selectivity on basis of isoforms and species may be helpful in better defining the structure–function determinants of the proteins of the SLC 15 family.