Hybrid PKS-NRPS synthetase; part of the gene cluster that mediates the biosynthesis of fusaridione A, a bright yellow trans-fused decalin-containing tetramic acid with antimicrobial activity (PubMed:23614392). The PKS module of fsdS catalyzes the formation of the polyketide unit which is then conjugated to L-tyrosine by the condensation domain of the fsdS NRPS module. Activity of the Dieckmann cyclase domain (RED) results in release of the intermediate fusaridione A (PubMed:23614392). The unstable pyrrolidinedione ring of fusaridione A is opened through a reverse-Dieckmann reaction to afford its ring-opened form (PubMed:23614392). Mycotoxin biosynthesis. 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 (By similarity). 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 (By similarity). Occasionally, epimerase (E) domains (responsible for l- to d-amino acid conversion) are present within the NRP synthetase (By similarity). FsdS contains also a polyketide synthase module (PKS) consisting of several catalytic domains including a ketoacyl synthase domain (KS), an acyl transferase domain (AT), a dehydratase domain (DH), a methyltransferase domain (MT), and a ketoreductase domain (KR) (PubMed:15724180, PubMed:23614392). Instead of a thioesterase domain (TE), fsdS finishes with a reductase-like domain (R) for peptide release (PubMed:15724180, PubMed:23614392). FsdS has the following architecture: KS-AT-DH-KR-PCP-C-A-T-R (PubMed:15724180, PubMed:23614392). In the C-terminal section; belongs to the NRP synthetase family.