The proton-coupled folate transporter (PCFT), a member (SLC46A1) of the superfamily of solute transporters, delivers folates into cells using the proton gradient as the energy source. It plays essential roles in the intestinal absorption of folates at the brush-border membrane of the proximal jejunum and transport of folates across the choroid plexus into the cerebrospinal fluid. Therefore, loss-of-function mutations in the PCFT gene result in the rare autosomal recessive disorder, hereditary folate malabsorption (HFM). PCFT is also highly expressed in a variety of carcinomas where it delivers antifolates to cancer cells within the acidic microenvironment of tumors. Among the antifolates, pemetrexed has the highest affinity for PCFT. Expression of PCFT is positively associated with the efficacy of pemetrexed in the treatment of pleural mesothelioma. Ongoing research is focused on two areas.

1. Characterization of the structure-function relationship of this transporter and the identification of amino acid residues that play a key role in its function. The substituted cysteine accessibility method (SCAM) is used to characterize the accessibility of residues within transmembrane domains and to define the aqueous translocation pathway. Special attentions will be given on residues that are involved in proton binding, proton-coupling, extracellular gating, folate substrate binding and locking/unlocking of transporter. Homology models of PCFT will be used to understand the structural ramifications of functional studies in the absence of a crystal structure of this protein.
2. Detection of novel loss-of-function PCFT mutations in patients with hereditary folate malabsorption (HFM). Genomic DNAs covering the exons of PCFT gene will be amplified and sequenced. Novel mutations will be identified and underlying mechanisms for defective folate transport will be characterized. These findings will complement the understanding of structure function relationship of PCFT.

Aluri, S., Zhao, R., Lin, K., Shin, D. S., Fiser, A., and Goldman, I. D. (2019) Substitutions that lock and unlock the proton-coupled folate transporter (PCFT-SLC46A1) in an inward-open conformation. J. Biol. Chem. 294, 7243-7258

Aluri, S., Zhao, R., Fiser, A., and Goldman, I. D. (2018) Substituted-cysteine accessibility and cross-linking identify an exofacial cleft in the 7(th) and 8(th) helices of the proton-coupled folate transporter (SLC46A1). Am. J. Physiol Cell Physiol 314, C289-C296

Zhao, R., Najmi, M., Aluri, S., Spray, D. C., and Goldman, I. D. (2018) Concentrative Transport of Antifolates Mediated by the Proton-Coupled Folate Transporter (SLC46A1); Augmentation by a HEPES Buffer. Mol. Pharmacol. 93, 208-215

Aluri, S., Zhao, R., Lubout, C., Goorden, S. M. I., Fiser, A., and Goldman, I. D. (2018) Hereditary folate malabsorption due to a mutation in the external gate of the proton-coupled folate transporter-SLC46A1. Blood Advances 2, 61-69

Zhao, R., Najmi, M., Aluri, S., and Goldman, I. D. (2017) Impact of post-translational modifications of engineered cysteines on the substituted cysteine accessibility method; evidence for glutathionylation. Am. J. Physiol Cell Physiol 312, 517-526

Najmi, M., Zhao, R., Fiser, A., and Goldman, I. D. (2016) Role of the tryptophan residues in proton-coupled folate transporter (PCFT-SLC46A1) function. Am. J. Physiol Cell Physiol 311, C150-C157

Zhao, R., Najmi, M., Fiser, A., and Goldman, I. D. (2016) Identification of an extracellular gate for the proton-coupled folate transporter (SLC46A1) by cysteine cross-linking. J. Biol. Chem. 291, 8162-8172

Zhao, R., Visentin, M., and Goldman, I. D. (2015) Determinants of the activities of antifolates delivered into cells by folate-receptor-mediated endocytosis. Cancer Chemother. Pharmacol. 75, 1163-1173

Visentin, M., Unal, E. S., Najmi, M., Fiser, A., Zhao, R., and Goldman, I. D. (2015) Identification of Tyr residues that enhance folate substrate binding and constrain oscillation of the proton-coupled folate transporter (PCFT-SLC46A1). Am. J. Physiol Cell Physiol 308, C631-C641

Zhao, R., Diop-Bove, N., and Goldman, I. D. (2014) Enhanced receptor-mediated endocytosis and cytotoxicity of a folic acid-desacetylvinblastine monohydrazide conjugate in a pemetrexed-resistant cell line lacking folate-specific facilitative carriers but with increased folate receptor expression. Mol Pharmacol. 85, 310-321