Hybrid PKS-NRPS synthetase; part of the gene cluster that mediates the biosynthesis of pyranterreones, a family of antioxidative compounds (PubMed:32077283). The first step of pyranonigrins biosynthesis is performed by the hybrid PKS-NRPS synthetase pytA that condenses 4 malonyl-CoA units ato the acetyl starter unit by the modular PKS of pytA (PubMed:32077283). The acyl chain is then connected to an L-serine through the amide bond by the modular NRPS of pytA (PubMed:32077283). A tetramic acid is formed and released from the PKS-NRPS pytA to give pyranterreone 5 with the help of the thioesterase pytI (PubMed:32077283). Pyranterreone 5 could be methylated by pytC to afford pyranterreone 6 (Probable). Both pyranterreones 5 and 6 are subsequently oxidized by the FAD-linked oxidoreductase pytB and the cytochrome P450 monooxygenase pytD to form the fused gamma-pyrone core, resulting in pyranterreones 7 and 11, respectively (PubMed:32077283). The hydroxy group at C-8 of pyranterreones 7 and 11 are dehydrated by the aspartyl protease pytH to form a delta-7 double bond to give pyranterreones 3 and 1, 2 accordingly (PubMed:32077283). The exo-methylene of pyranterreone 3 could be reduced into a pendant methyl by reductase pytE to provide pyranterreone 4, also known as cordylactam (Probable). Pyranterreone 4 can be reconverted to pyranterreone 3 through pytB-catalyzed dehydrogenation or further oxidized to pyranterreones 9 and 10 (Probable). Secondary metabolite biosynthesis. Expression is positively regulated by the cluster-specific transcription factor pytR. The N-terminal part acts as a polyketide synthase and includes a ketosynthase (KS) domain that catalyzes repeated decarboxylative condensation to elongate the polyketide backbone; a malonyl-CoA:ACP transacylase (MAT) domain that selects and transfers the extender unit malonyl-CoA; a dehydratase (DH) domain that reduces hydroxyl groups to enoyl groups; an enoylreductase (ER) domain that reduces enoyl groups to alkyl group; a ketoreductase (KR) domain that catalyzes beta-ketoreduction steps; and an acyl-carrier protein (ACP) that serves as the tether of the growing and completed polyketide via its phosphopantetheinyl arm. The C-terminal part acts as an NRP synthetase 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. PytA contains one module and terminates in a thioesterase domain (TE) that releases the newly synthesized peptide from the enzyme. Impairs the production of pyranterreones. In the C-terminal section; belongs to the NRP synthetase family. In A.terreus strain NIH2624, ATEG_00913 misses most of its catalytic domains. This difference may be due to errors in the sequencing or the automatic annotation of genome. The protein consists of a highly reducing PKS module (KS-AT-DH-ER-KR-ACP), a single NRPS module (C-A-PCP), and C-terminal TD domain.