Catalyzes the synthesis of gamma-glutamylcysteine (gamma-GC) (PubMed:16262797). This compound is used as substrate for the biosynthesis of the low-molecular thiol compound ergothioneine (By similarity). ATP + L-cysteine + L-glutamate = ADP + gamma-L-glutamyl-L-cysteine + H(+) + phosphate Weakly inhibited by L-methionine-S,R-sulphoximine (MSO) and strongly inhibited by D,L-buthionine-S,R-sulphoximine (BSO) in vitro. Amino-acid biosynthesis; ergothioneine biosynthesis. Was identified as a high-confidence drug target. Belongs to the glutamate--cysteine ligase type 2 family. EgtA subfamily.