Biosynthesis

The biosynthesis of L-ergothione L-EGT was initially isolated from ergot fungi by Tanret et al. in 1909, and it was believed that L-EGT was distributed in conidia rather than sclerotium. Heath and Wildy confirmed that histidine and methionine were precursors of L-EGT synthesis in 1956, 1957 and 1958 by successively labeling methionine with acetate, [35S] and [2 (ring) - 14C] with histamine [18] and [19]. In 1959, Melville et al. [20] studied the pathway of biosynthesis of L-EGT trimethylammonium groups by Neurospora crassa with the help of isotope labeled precursors; It is speculated that the biosynthesis sequence of L-EGT is as follows: histidine is synthesized by methionine methylation to histidine betaine, and then L-EGT is synthesized by cysteine thiolation.

Ishikawa et al. used the cell-free extract of Streptomyces rough to catalyze the synthesis of histidine α- Methylation of amino nitrogen atoms, speculated to be catalyzed by N-dimethylhistidine methyltransferase α- N-methylhistidine α- N forms histidine trimethyl salt, where the dimethylhistidine methyltransferase is responsible for the three transamination methylation reactions of histidine conversion to histidine trimethyl salt . Until 2010, Seeback et al（ γ- Glutacyl cysteine ligase, EgtB (Fe 2+dependent enzyme), EgtC (glutamyl aminotransferase), EgtD (histidine methyltransferase), and EgtE (PLP dependent C-S lyase)  (marked with "*" in Figure 2).

Firstly, in bacterial synthesis, EgtD transfers three methyl groups from s-adenosylmethionine (SAM) to histidine to form histidine trimethyl salt; Meanwhile, Egta converts cysteine into γ- Glutamic acid cysteine. Secondly, with divalent ions and oxygen as cofactor γ- Generation of glutamyl cysteine catalyzed by EgtB γ- Glutamoyl hexynylcysteine sulfoxide. Subsequently, γ- The glutamyl hexyne cysteine sulfoxide is catalyzed by EgtC to form hexene cysteine sulfoxide. Finally, hexene cysteine sulfoxide is catalyzed by Egte to produce L-EGT, while releasing pyruvate and NH3.

In addition, the latest study found that the biosynthesis of L-EGT in Mycobacterium strains only requires three steps, namely EgtD → MsEgtB (marked with "#" in Figure 2) → EgtE; MsEgtB can utilize cysteine as a sulfur donor to convert histidine trimethyl lactone into hexene cysteine sulfoxide, reducing the L-EGT biosynthesis pathway of bacteria from 5 steps to 3 steps .

Therefore, this shorter bacterial synthesis pathway with a specific EgtB is more attractive for the biological preparation of L-EGT. In cyanobacteria and anaerobic green sulfur bacteria, the synthesis pathway of L-EGT is composed of two enzymes, EanA and EanB [27, 28] (labeled with "Λ" in Figure 2). Histidine is converted into histidine trimethyl lactone under the action of EanA enzyme, and directly catalyzed by EanB enzyme to generate L-EGT. In some fungi, such as Streptomyces scabra, Schizosaccharomyces, Aspergillus fumigatus, and Rhodotorula, the L-EGT synthesis pathway is different from that of Mycobacterium smegmae, cyanobacteria, and anaerobic green sulfur bacteria [29,30]. This pathway is composed of two synthetases, Egt1 and Egt2 (marked with "&" in Figure 2).

Among these four fungi, Egt1 transfers three methyl groups from s-adenosylmethionine (SAM) to histidine to form histidine trimethyl lactone, and further catalyzes the formation of histidine trimethyl lactone using oxygen and cysteine to form hexene cysteine sulfoxide. Finally, Egt2 catalyzes the formation of L-EGT [35]. In addition, the fungal L-EGT biosynthesis pathway also eliminates the need for γ- The participation of glutamyl cysteine eliminates the biosynthetic competition between L-EGT and glutathione, greatly improving the biosynthetic efficiency of L-EGT.