The superfamily keeps growing: Identification in trypanosomatids of RibJ, the first riboflavin transporter family in protists

Abstract

BackgroundTrypanosomatid parasites represent a major health issue affecting hundreds of million people worldwide, with clinical treatments that are partially effective and/or very toxic. They are responsible for serious human and plant diseases including Trypanosoma cruzi (Chagas disease), Trypanosoma brucei (Sleeping sickness), Leishmania spp. (Leishmaniasis), and Phytomonas spp. (phytoparasites). Both, animals and trypanosomatids lack the biosynthetic riboflavin (vitamin B2) pathway, the vital precursor of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) cofactors. While metazoans obtain riboflavin from the diet through RFVT/SLC52 transporters, the riboflavin transport mechanisms in trypanosomatids still remain unknown.Methodology/Principal findingsHere, we show that riboflavin is imported with high affinity in Trypanosoma cruzi, Trypanosoma brucei, Leishmania (Leishmania) mexicana, Crithidia fasciculata and Phytomonas Jma using radiolabeled riboflavin transport assays. The vitamin is incorporated through a saturable carrier-mediated process. Effective competitive uptake occurs with riboflavin analogs roseoflavin, lumiflavin and lumichrome, and co-factor derivatives FMN and FAD. Moreover, important biological processes evaluated in T. cruzi (i.e. proliferation, metacyclogenesis and amastigote replication) are dependent on riboflavin availability. In addition, the riboflavin competitive analogs were found to interfere with parasite physiology on riboflavin-dependent processes. By means of bioinformatics analyses we identified a novel family of riboflavin transporters (RibJ) in trypanosomatids. Two RibJ members, TcRibJ and TbRibJ from T. cruzi and T. brucei respectively, were functionally characterized using homologous and/or heterologous expression systems.Conclusions/SignificanceThe RibJ family represents the first riboflavin transporters found in protists and the third eukaryotic family known to date. The essentiality of riboflavin for trypanosomatids, and the structural/biochemical differences that RFVT/SLC52 and RibJ present, make the riboflavin transporter -and its downstream metabolism- a potential trypanocidal drug target.

RibU is an essential determinant of Listeria pathogenesis that mediates acquisition of FMN and FAD during intracellular growth

“…Many organisms encode transporters that allow them to obtain riboflavin from the environment ( 5 – 8 ). Several bacterial and all eukaryotic intracellular pathogens require an exogenous source of riboflavin ( 9 – 11 ), and interestingly, some also lack the enzymes that catalyze the conversion of riboflavin to FMN and FAD ( 11 , 12 ). How these riboflavin auxotrophic intracellular pathogens fulfill their flavin requirement in host cells is poorly understood.…”

How much (ATP) does it cost to build a trypanosome? A theoretical study on the quantity of ATP needed to maintain and duplicate a bloodstream-formTrypanosoma bruceicell

“…Trypanosomes also need vitamins and other micronutrients whose biosynthetic processes and/or uptake require ATP. Mechanisms for uptake from the medium have been identified for choline (Macêdo et al, 2013), pyridoxine (vitamin B6) (Gray, 1995) and riboflavin (vitamin B2) (Balcazar et al, 2017). Ascorbic acid (vitamin C) biosynthesis has been identified in T. brucei , with the last step taking place within glycosomes (Wilkinson et al, 2005).…”

Efficient flavinylation of glycosomal fumarate reductase by its own ApbE domain in Trypanosoma brucei

“…Can we envisage a metabolic reason for the benefit of a more efficient cis ‐flavinylation of FRD in some organisms? Limited availability or transport of riboflavin [54] is a possibility, as trypanosomes are riboflavin auxotrophs. Most importantly, they depend on metabolic flexibility and adaptation to rapidly changing host environments in their parasitic life cycle.…”