The Molecular Evolution of Ergothioneine Biosynthesis and Transport and its Role in Human Health

Ergothioneine is a histidine-derived amino acid, which intracellularly functions as an anti-inflammatory antioxidant, with accumulating evidence for impacts on human cardiovascular health. A dietary nutrient, ergothioneine is found enrich in mushrooms and fermented foods , to date no randomised trials have examined its efficacy for metabolic syndrome. Ergothioneine biosynthesis, currently, has been believed to be limited to specific bacteria and fungi. During this process, sulfoxide synthases specifically, are indispensable. However, no research has comprehensively examined the molecular evolution of sulfoxide synthases across the kingdoms of life. Up until 2020, only one transporter had been identified for ergothioneine, namely the solute carrier 22A member 4 (SLC22A4). With the de-orphaning of a second mammalian transport of ergothioneine in 2020 (the solute carrier 22A member 15; SLC22A15), and identification of novel ATP-binding cassette (ABC) microbial importers of ergothioneine (EgtU and EgtUV) in 2022; and the first microbial exporter of ergothioneine (mfsT1), it has become clear that additional ergothioneine transporters undoubtedly exist across the kingdoms of life.

Therefore, this project aimed, firstly, to design a human study that supplements ergothioneine to the metabolic syndrome risk group for 12 weeks, secondly, to investigate the molecular evolution of sulfoxide synthases that are related to EgtB, and thirdly, to explore the molecular evolution of ergothioneine import and export transporters across the kingdoms of life. The phylogenetic analysis of sulfoxide synthases evolution identified 7 groups of sulfoxide synthases, including 5 types of EgtB, namely Type I to V EgtB. Among these EgtB sequences, Type I EgtB is similar to SenA, whereas Type IV EgtB is similar to OvoA. The phylogenetic analysis of ergothioneine transporters demonstrated several SLC transporters, including SLC1-5, SLC16, SLC17, SLC19, SLC22, SLC29, SLC52, whereas SLC19 transporters are the most similar to mfsT1.

In conclusion, the phylogenetic tree in Chapter 3 identified five types of EgtB and three types of OvoA among sulfoxide synthase homologues. Moreover, utilising the molecular evolution workflow, unrooted phylogenetic trees in Chapter 4 demonstrated several SLC transporters in the homologues of EgtUV and mfsT1, and that SLC19 transporters are the most likely candidate mammalian ergothioneine exporter.