Probably catalyzes the conversion of hercynylcysteine sulfoxide to ergothioneine. Ergothioneine is a secreted antioxidant that protects mycobacterium from oxidative stress. AH2 + H(+) + S-(hercyn-2-yl)-L-cysteine S-oxide = A + ergothioneine + NH4(+) + pyruvate Amino-acid biosynthesis; ergothioneine biosynthesis. Belongs to the class-V pyridoxal-phosphate-dependent aminotransferase family. EgtE subfamily. Truncated N-terminus.