Functional Study of the Human Riboflavin Transporter 2 Using Proteoliposomes System

Riboflavin is essential for cell viability. The biologically active forms of riboflavin, FMN and FAD, participate in many biochemical redox reactions including the metabolism of carbohydrates, amino acids, and lipids. Differently from bacteria, fungi, and plants which synthesize riboflavin, higher organisms have lost the ability to synthesize the vitamin and must absorb it from food and intestinal microflora production. The riboflavin flux through cell membranes occurs via specific transporters belonging to the SLC52 family. Three members of this family have been identified so far which show poor homology with the riboflavin transporters of Saccharomyces cerevisiae or bacteria. Alterations of RFVTs are causative of severe diseases. Indeed, under pathological stress, humans are susceptible of developing riboflavin deficiency. Such a deficiency in pregnancy induces fetus abnormalities, and has been indicated as a risk factor for anemia, cancer, cardiovascular diseases, and neurodegeneration. Moreover, inherited diseases are also of interest; the most well-described is the Brown–Vialetto–van Laere syndrome, a rare neurological disorder characterized by infancy onset sensorineural deafness and pontobulbar palsy. Numerous polymorphisms of Slc52a2 and Slc52a3 genes associated with this syndrome have been discovered. In spite of their important metabolic role and their relevance to human health, the riboflavin transporters are still poorly characterized. Bacterial overexpression, purification, and protein reconstitution in liposomes represent an up-to-date methodology for obtaining functional data information. The methodology for reconstituting the RFVT2 into proteoliposomes and performing transport assay is described. These methods will be suitable for investigating the functional defects of the variants of RFVTs associated with human pathologies.