Folate receptor endocytosis and trafficking.

Folate absorption is primarily mediated by a membrane transporter with micro-molar affinities for folates. Paradoxically, folates are only present at low nanomolar concentrations in extracellular milieus; membrane folate receptors (FRs) with nanomolar affinities for folates are likely to substantially modulate folate availability for these transporters. Functional isoforms of FRs are anchored to the membrane by a glycolipid anchor, the glycosylphosphatidylinositol (GPI) anchor. In this chapter we discuss recent insights that have been obtained with regards to GPI-anchored protein trafficking in the context of folate transport via the GPI-anchored FR. Specifically, we focus on recent advances in elucidating the pathways and mechanisms of endocytic sorting of the GPI-anchored FR, and the connection with membrane rafts.