Mediates the Na(+)- and Cl(-)-dependent uptake of imino acids such as L-proline, N-methyl-L-proline and pipecolate as well as N- methylated amino acids (PubMed:15632147, PubMed:19033659, PubMed:33428810). Also transports glycine, regulates proline and glycine homeostasis in the brain playing a role in the modulation of NMDAR currents (PubMed:33428810). {ECO:0000269|PubMed:15632147, ECO:0000269|PubMed:19033659, ECO:0000269|PubMed:33428810}. This is the function of SLC6A20 (solute carrier family 6 member 20, Ensembl gene identifier ENSG00000163817).