Nonribosomal peptide synthetase; part of the gene cluster that mediates the biosynthesis of oxepinamides, derivatives of anthranilyl-containing tripeptides that share an oxepin ring and a fused pyrimidinone moiety (PubMed:33004788). The nonribosomal peptide synthetase (NRPS) opaA assembles the quinazolinone core with D-Phe incorporation (PubMed:33004788). The first adenylation domain (A1) of opaA loads and activates anthranilic acid whereas the second A domain (A2) is for activating of L-Phe, which is then converted to D-form by the E domain (PubMed:33004788). The third A domain (A3) is responsible for L-Ile activation and the terminal condensation domain C3 for cyclization and releasing the NRPS product protuboxepin K (PubMed:33004788). The cytochrome P450 monooxygenase opaB then catalyzes alone the oxepin ring formation to convert protuboxepin K into protuboxepin A (PubMed:33004788). The flavoenzyme opaC installs subsequently one hydroxyl group at the oxepin ring, accompanied by double bond migration, to form 15-epi-oxepinamide E (PubMed:33004788). The epimerase opaE changes the D-Phe residue back to L-form, leading to oxepinamide E, which is further methylated at the hydroxyl group at C-12 by the O-methyltransferase OpaF to yield oxepinamide F (PubMed:33004788). NRP synthetases are composed of discrete domains (adenylation (A), thiolation (T) or peptidyl carrier protein (PCP) and condensation (C) domains) which when grouped together are referred to as a single module. Each module is responsible for the recognition (via the A domain) and incorporation of a single amino acid into the growing peptide product. Thus, an NRP synthetase is generally composed of one or more modules and can terminate in a thioesterase domain (TE) that releases the newly synthesized peptide from the enzyme. Occasionally, epimerase (E) domains (responsible for L- to D- amino acid conversion) are present within the NRP synthetase. OpaA has the following architecture: A1-T1-C1-A2-T2-E-C2-A3-T3-C3. Abolishes the production of both oxepinamide F and oxepinamide E. Belongs to the NRP synthetase family.