Isolation and characterization of a folate receptor from human placenta

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Folate binding proteins (FBPs) are present in serum and various tissues, but their functions remain largely unknown.
• Understanding the role of FBPs is crucial for comprehending folate metabolism and transport.

Purpose of the Study:

• To isolate and characterize a particulate folate binding protein from human placenta.
• To investigate the potential function of this placental FBP, particularly its relationship to other known FBPs and its presence on cell surfaces.

Main Methods:

• Solubilization of particulate placental FBP using Triton X-100.
• Purification via affinity chromatography using pteroylglutamic acid-Sepharose.
• Characterization using SDS-PAGE, binding stoichiometry analysis, and glycoprotein analysis.
• Antibody generation and immunological assays (immunodiffusion, immunoprecipitation, immunofluorescence).

Main Results:

• A placental FBP was purified 61,000-fold, yielding a single band of Mr = 38,500 on SDS-PAGE.
• The purified protein bound 1 mole of folate per mole of protein and was identified as a glycoprotein (12% carbohydrate).
• Immunological studies revealed shared antigenic determinants with human milk FBPs and the presence of a similar protein on human erythrocyte plasma membranes.

Conclusions:

• The purified placental folate binding protein is antigenically related to human milk FBPs.
• The presence of an immunologically similar protein on erythrocyte membranes suggests a potential role as a folate receptor.