Differential stereospecificities and affinities of folate receptor isoforms for folate compounds and antifolates

Biochem Pharmacol. 1992 Nov 3;44(9):1898-901. doi: 10.1016/0006-2952(92)90089-2.


Two membrane folate receptor (MFR) isoforms are present in human tissues i.e. MFR-1 (e.g. placenta) and MFR-2 (e.g. placenta, KB cells, CaCo-2 cells). MFR-1 was expressed in COS-1 cells and the resulting protein had the same polypeptide molecular weight as the native protein. The affinities of (6S) and (6R) diastereoisomers of N5-methyltetrahydrofolate, N5-formyltetrahydrofolate, and 5,10-dideazatetrahydrofolate as well as folic acid and methotrexate to MFR-1, MFR-2 and placental MFR (MFR-1 plus MFR-2) were determined in terms of the Ki values for their competitive inhibition of the binding of [3H]folic acid to these proteins. The results indicated a striking difference in the stereospecificity of MFR-1 and MFR-2 for reduced folate coenzymes; MFR-2 preferentially bound to the physiological (6S) diastereoisomers and MFR-1 bound preferentially to the unphysiological (6R) diastereoisomers, while dideazatetrahydrofolate did not show significant stereospecificity for MFR-1. Furthermore, MFR-2 displayed significantly (2- to 100-fold) greater affinities for all the compounds tested compared to MFR-1. Purified placental MFR, a natural source of MFR-1 which contains variable amounts of MFR-2, showed intermediate Ki values for the compounds tested compared with MFR-1 and MFR-2 and stereospecificities similar to MFR-1. These observations demonstrate striking differences in the ligand binding sites of MFR-1 and MFR-2 which could potentially be exploited in the design of MFR isoform specific antifolates.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Binding, Competitive
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Carrier Proteins / physiology
  • DNA / genetics
  • Female
  • Folate Receptors, GPI-Anchored
  • Folic Acid / metabolism*
  • Folic Acid Antagonists / metabolism*
  • Haplorhini
  • Humans
  • KB Cells
  • Kinetics
  • Leucovorin / metabolism
  • Methotrexate / metabolism
  • Placenta / ultrastructure
  • Receptors, Cell Surface*
  • Stereoisomerism
  • Tetrahydrofolates / metabolism


  • Carrier Proteins
  • Folate Receptors, GPI-Anchored
  • Folic Acid Antagonists
  • Receptors, Cell Surface
  • Tetrahydrofolates
  • lometrexol
  • DNA
  • Folic Acid
  • Leucovorin
  • 5-methyltetrahydrofolate
  • Methotrexate