Transports L-serine, L-threonine and L-cysteine with high affinity (PubMed:23144255, PubMed:25535271). Stereoselective, with a strong preference for L-serine. Is the main L-serine transporter and is responsible for optimal growth in media containing free amino acids as the sole source of amino acids. Is also the main transporter for L-threonine (PubMed:25535271). Deletion mutant shows a significant growth defect in medium that contains only free amino acids as a source of amino acids. Mutant shows a strong decrease in L-serine uptake and cannot transport L-threonine. Can still transport L-alanine. SerP1/serP2 double mutant is completely devoid of uptake activity of either L-serine, L-threonine or L-alanine. Belongs to the amino acid-polyamine-organocation (APC) superfamily. Amino acid transporter (AAT) (TC 2.A.3.1) family.