7e5t | pdb_00007e5t
Crystal structure of Fsa2
Structural highlights
Function[FSA2_FUSSF] Diels-Alderase; part of the gene cluster that mediates the biosynthesis of equisetin and fusarisetin A, 2 trans-fused decalin-containing tetramic acids with antimicrobial activity (PubMed:25770422). The PKS module of fsa1 together with the enoylreductase fsa3 catalyze the formation of the polyketide unit which is then conjugated to L-serine by the condensation domain of the fsa1 NRPS module (PubMed:25770422). Activity of the Dieckmann cyclase domain (RED) results in release of the intermediate N-desmethylequisetin also called trichosetin (PubMed:25770422). Diels-Alderase fsa2 is involved in endo-selective Diels-Alder cycloaddition to form the decalin ring of equisetin (PubMed:25770422, PubMed:28401214). Subsequent N-methylation is carried out by fsa4 to give equisetin (PubMed:25770422). The enzymatic gene responsible for the conversion of equisetin to fusarisetin A has not been identified yet and is probably located outside of the fsa cluster (PubMed:28401214).[1] [2] Publication Abstract from PubMedEnzymes catalyzing [4+2] cycloaddition have attracted increasing attention because of their key roles in natural product biosynthesis. Here, we solved the X-ray crystal structures of a pair of decalin synthases, Fsa2 and Phm7, that catalyze intramolecular [4+2] cycloadditions to form enantiomeric decalin scaffolds during biosynthesis of the HIV-1 integrase inhibitor equisetin and its stereochemical opposite, phomasetin. Computational modeling, using molecular dynamics simulations as well as quantum chemical calculations, demonstrates that the reactions proceed through synergetic conformational constraints assuring transition state-like substrates folds and their stabilization by specific protein-substrate interactions. Site-directed mutagenesis experiments verified the binding models. Intriguingly, the flexibility of bound substrates is largely different in two enzymes, suggesting the distinctive mechanism of dynamics regulation behind these stereoselective reactions. The proposed reaction mechanism herein deepens the basic understanding how these enzymes work but also provides a guiding principle to create artificial enzymes. Molecular basis for two stereoselective Diels-Alderases that produce decalin skeletons.,Fujiyama K, Kato N, Re S, Kinugasa K, Watanabe K, Takita R, Nogawa T, Hino T, Osada H, Sugita Y, Takahashi S, Nagano S Angew Chem Int Ed Engl. 2021 Jun 13. doi: 10.1002/anie.202106186. PMID:34121297[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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