ATP-dependent carboxylate-amine ligase which exhibits weak glutamate--cysteine ligase activity. However, because of the low catalytic rate, the question remains whether L-cysteine is the actual biological substrate. ATP + L-cysteine + L-glutamate = ADP + gamma-L-glutamyl-L-cysteine + H(+) + phosphate Homodimer. Catalytic activity was tested towards all 20 common amino acids, but was only observed with L-cysteine. Belongs to the glutamate--cysteine ligase type 2 family. YbdK subfamily.