Part of the bacABCDEFG operon responsible for the biosynthesis of bacilysin, an irreversible inactivator of the glutaminase domain of glucosamine synthetase. Catalyzes the formation of alpha-dipeptides from various L-amino acids in the presence of ATP. In vivo catalyzes the ligation of L-alanine and L-anticapsin (epoxycyclohexanonyl-Ala) to produce the final bacilysin antibiotic (L-Ala-L-4S-cyclohexenonyl-Ala dipeptide). The substrate specificity is restricted to small amino acids such as L-Ala, for the N-terminal end of the dipeptide, whereas a wide range of hydrophobic amino acids such as L-Phe, L-Tyr and L-Met are recognized for the C-terminal end. ATP + L-alanine + L-anticapsin = ADP + bacilysin + H(+) + phosphate Binds 2 Mg(2+) ions per monomer. kcat is 9.32 sec(-1) for ligase activity with alanine as substrate (PubMed:24702628). kcat is 10.4 sec(-1) for ligase activity with phenylalanine as substrate (PubMed:24702628). kcat is 630 min(-1) for ligase activity with alanine and phenylalanine as substrate (PubMed:22407814). Optimum pH is 9.5. Optimum temperature is 37 degrees Celsius. Antibiotic biosynthesis; bacilysin biosynthesis. Monomer or homodimer. The compound guanosine 5'-diphosphate 3'-diphosphate (ppGpp) is essential for the transcription of the bacABCDE operon and GTP regulates the transcription of both this operon and ywfH via the CodY-mediated regulation system.