Involved in the biosynthesis of terminal alkyne-containing amino acids such as L-beta-ethynylserine, that are produced as antibiotics by S.cattleya. Catalyzes the ATP-dependent ligation of L-propargylglycine to L-glutamate to form the dipeptide L-gamma-glutamyl-L-propargylglycine. Is selective for L-propargylglycine over norvaline, allylglycine and the standard proteinogenic amino acids, except L-cysteine which can be used as a substrate to a lesser extent. ATP + L-glutamate + L-propargylglycine = ADP + H(+) + L-gamma-glutamyl-L-propargylglycine + phosphate kcat is 2.0 sec(-1) for the glutamylation of L-propargylglycine. kcat is 1.53 sec(-1) for the glutamylation of L-cysteine. Amino-acid metabolism. Antibiotic biosynthesis. Cells lacking this gene produce lowered levels of both L-propargylglycine and L-beta-ethynylserine, that are terminal alkyne-containing amino acids produced by wild-type S.cattleya.