Reaction: 4-nitrobenzoyl-CoA + malonyl-CoA + 6 (S)-methylmalonyl-CoA + 6 NADPH + 4 H+ = demethyldeoxyspectinabilin + 7 CO2 + 8 CoA + 6 NADP+ + 5 H2O
For diagram of reaction, click here
Glossary: demethyldeoxyspectinabilin = 2-hydroxy-3,5-dimethyl-6-[(3E,5E,7E,9E)-3,5,7,9-tetramethyl-10-(4-nitrophenyl)deca-3,5,7,9-tetraen-1-yl]pyran-4-one
spectinabilin = 2-methoxy-3,5-dimethyl-6-[(2R,4Z)-4-[(2E,4E,6E)-2,4,6-trimethyl-7-(4-nitrophenyl)hepta-2,4,6-trien-1-ylidene]oxolan-2-yl]pyran-4-one
Other name(s): norAA’BC (gene names); spectinabilin polyketide synthase complex
Systematic name: malonyl-CoA/(S)-methylmalonyl-CoA:4-nitrobenzoyl-CoA (methyl)malonyltransferase (demethyldeoxyspectinabilin-forming)
Comments: This polyketide synthase, characterized from the bacteria Streptomyces orinoci and Streptomyces spectabilis, generates the backbone of the antibiotic spectinabilin. It is composed of 6 modules that total 28 domains and is encoded by four genes. The enzyme accepts the unusual starter unit 4-nitrobenzoyl-CoA and extends it by 6 molecules of (S)-methylmalonyl-CoA and a single molecule of malonyl-CoA. The first module (encoded by norA) is used twice in an iterative fashion, so that the seven Claisen condensation reactions are catalysed by only six modules. The iteration becomes possible by the transfer of the [acp]-bound polyketide intermediate back to the ketosynthase (KS) domain on the opposite polyketide synthase strand (polyketides are homodimeric).
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Traitcheva, N., Jenke-Kodama, H., He, J., Dittmann, E. and Hertweck, C. Non-colinear polyketide biosynthesis in the aureothin and neoaureothin pathways: an evolutionary perspective. Chembiochem 8 (2007) 1841-1849. [PMID: 17763486]
2. Choi, Y.S., Johannes, T.W., Simurdiak, M., Shao, Z., Lu, H. and Zhao, H. Cloning and heterologous expression of the spectinabilin biosynthetic gene cluster from Streptomyces spectabilis. Mol. Biosyst. 6 (2010) 336-338. [PMID: 20094652]