Probably catalyzes the conversion of hercynylcysteine sulfoxide to ergothioneine (By similarity). ERG is one of the major redox buffers which protects bacteria against redox stressors and antibiotics; loss of ERG or mycothiol (MSH, the other major redox buffer in this bacteria) leads to respiratory alterations and bioenergetic deficiencies that negatively impact virulence (PubMed:26774486). AH2 + H(+) + S-(hercyn-2-yl)-L-cysteine S-oxide = A + ergothioneine + NH4(+) + pyruvate Amino-acid biosynthesis; ergothioneine biosynthesis. Not part of the egtA-egtB-egtC-egtD operon (PubMed:26774486). Belongs to the class-V pyridoxal-phosphate-dependent aminotransferase family. EgtE subfamily.