In silico Investigation on Structure–Function Relationship of Members Belonging to the Human SLC52 Transporter Family

Riboflavin is an essential water-soluble vitamin provided via the diet and converted into flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), important cofactors in the electron transport chain and other metabolic pathways. The adsorption and distribution of riboflavin is mediated by transmembrane transporters of the SLC52 family, namely RFVT1-3, whose mutations are mainly associated with two diseases: Multiple Acyl-CoA dehydrogenase deficiency (MADD) and the Brown-Vialetto-Van Laere (BVVL) syndrome. Moreover, these transporters are overexpressed in certain cancer cells, possibly due to the increased energetic demand, and are considered promising targets for cancer therapy. In this context, the goal of this work was to obtain reliable 3D structures of the RFVT1-3 proteins via the most innovative AI-based modelling methods (namely AlphaFold, RoseTTAFold and RosettaTR). This is a crucial step toward the understanding of the recognition and transport mechanism of these transporters, and, therefore, towards the development of inhibitors which could be used as anticancer drugs. Additionally, the generated models were used to test the affinity of riboflavin for these transporters and the effect of two well-known mutations related to BVVL on riboflavin recognition via molecular docking and molecular dynamics simulations. A mechanistic hypothesis of the role of the two RFVT2 and RFVT3 mutations in the decrease of riboflavin transport, specifically via the decrease of riboflavin affinity, was proposed. Future studies will be focused on the identification of promising compounds that could act as transport inhibitors binding to the recognition site of riboflavin identified in this study.