Folylpoly-γ-glutamate Carboxypeptidase from Pig Jejunum

Jejunal folylpoly-gamma-glutamate carboxypeptidase hydrolyzes dietary folates prior to their intestinal absorption. The complete folylpoly-gamma-glutamate carboxypeptidase cDNA was isolated from a pig jejunal cDNA library using an amplified homologous probe incorporating primer sequences from prostate-specific membrane antigen, a protein capable of folate hydrolysis. The cDNA encodes a 751-amino acid polypeptide homologous to prostate-specific membrane antigen and rat brain N-acetylated alpha-linked acidic dipeptidase. PC3 transfectant membranes exhibited activities of folylpoly-gamma-carboxypeptidase and N-acetylated alpha-linked acidic dipeptidase, while immunoblots using monoclonal antibody to native folylpoly-gamma-glutamate carboxypeptidase identified a glycoprotein at 120 kDa and a polypeptide at 84 kDa. The kinetics of native folylpoly-gamma-carboxypeptidase were expressed in membranes of PC3 cells transfected with either pig folylpoly-gamma-carboxypeptidase or human prostate-specific membrane antigen. Folylpoly-gamma-carboxypeptidase transcripts were identified at 2.8 kilobase pairs in human and pig jejunum, human and rat brain, and human prostate cancer LNCaP cells. Thus, pig folylpoly-gamma-carboxypeptidase, rat N-acetylated alpha-linked acidic dipeptidase, and human prostate-specific membrane antigen appear to represent varied expressions of the same gene in different species and tissues. The discovery of the jejunal folylpoly-gamma-carboxypeptidase gene provides a framework for future studies on relationships among these proteins and on the molecular regulation of intestinal folate absorption.