Engineering energetically efficient transport of dicarboxylic acids in yeast .

Biobased C4-dicarboxylic acids are attractive sustainable precursors for polymers and other materials. Commercial scale production of these acids at high titers requires efficient secretion by cell factories. In this study, we characterized 7 dicarboxylic acid transporters in oocytes and in engineered for dicarboxylic acid production. Among the tested transporters, the Mae1(p) from had the highest activity toward succinic, malic, and fumaric acids and resulted in 3-, 8-, and 5-fold titer increases, respectively, in , while not affecting growth, which was in contrast to the tested transporters from the tellurite-resistance/dicarboxylate transporter (TDT) family or the Na coupled divalent anion-sodium symporter family. Similar to Mae1(p), its homolog in Dct(p), increased the malate titer 12-fold without affecting the growth. Phylogenetic and protein motif analyses mapped Mae1(p) and Dct(p) into the voltage-dependent slow-anion channel transporter (SLAC1) clade of transporters, which also include plant Slac1(p) transporters involved in stomata closure. The conserved phenylalanine residue F329 closing the transport pore of Mae1(p) is essential for the transporter activity. The voltage-dependent SLAC1 transporters do not use proton or Na motive force and are, thus, less energetically expensive than the majority of other dicarboxylic acid transporters. Such transporters present a tremendous advantage for organic acid production via fermentation allowing a higher overall product yield.