Accepted name: (phenol)carboxyphthiodiolenone synthase
Reaction: (1) 3 malonyl-CoA + 2 (S)-methylmalonyl-CoA + icosanoyl-[(phenol)carboxyphthiodiolenone synthase] + 5 NADPH = C32-carboxyphthiodiolenone-[(phenol)carboxyphthiodiolenone synthase] + 5 CoA + 5 NADP+ + 5 CO2 + 2 H2O
(2) 3 malonyl-CoA + 2 (S)-methylmalonyl-CoA + docosanoyl-[(phenol)carboxyphthiodiolenone synthase] + 5 NADPH = C34-carboxyphthiodiolenone-[(phenol)carboxyphthiodiolenone synthase] + 5 CoA + 5 NADP+ + 5 CO2 + 2 H2O
(3) 3 malonyl-CoA + 2 (S)-methylmalonyl-CoA + 19-(4-hydroxyphenyl)-nonadecanoyl-[(phenol)carboxyphthiodiolenone synthase] + 5 NADPH = C37-(phenol)carboxyphthiodiolenone-[(phenol)carboxyphthiodiolenone synthase] + 5 CoA + 5 NADP+ + 5 CO2 + 2 H2O
(4) 3 malonyl-CoA + 2 (S)-methylmalonyl-CoA + 17-(4-hydroxyphenyl)heptadecanoyl-[(phenol)carboxyphthiodiolenone synthase] + 5 NADPH = C35-(phenol)carboxyphthiodiolenone-[(phenol)carboxyphthiodiolenone synthase] + 5 CoA + 5 NADP+ + 5 CO2 + 2 H2O
Glossary: C32-carboxyphthiodiolenone = (4E,9R,11R)-9,11-dihydroxy-2,4-dimethyl-3-oxotriacont-4-enoate
C34-carboxyphthiodiolenone = (4E,9R,11R)-9,11-dihydroxy-2,4-dimethyl-3-oxodotriacont-4-enoate
C35-phenolcarboxyphthiodiolenone = (4E)-9,11-dihydroxy-27-(4-hydroxyphenyl)-2,4-dimethyl-3-oxoheptacos-4-enoate
C37-phenolcarboxyphthiodiolenone = (4E,9R,11R)-9,11-dihydroxy-29-(4-hydroxyphenyl)-2,4-dimethyl-3-oxononacos-4-enoate
phthiocerols = linear carbohydrates containing one methoxyl group, one methyl group, and two secondary hydroxyl groups that serve as a backbone for certain lipids and glycolipids found in many species of Mycobacteriaceae
Other name(s): ppsABCDE (gene names)
Systematic name: (methyl)malonyl-CoA:long-chain acyl-[(phenol)carboxyphthiodiolenone synthase] (methyl)malonyltransferase {carboxyphthiodiolenone-[(phenol)carboxyphthiodiolenone synthase]-forming}
Comments: The enzyme, which is a complex of five polyketide synthase proteins, is involved in the synthesis of the lipid core common to phthiocerols and phenolphthiocerols. The first protein, PpsA, can accept either a C18 or C20 long-chain fatty acyl, or a (4-hydroxyphenyl)-C17 or C19 fatty acyl. The substrates must first be adenylated by EC, long-chain fatty acid adenylase/transferase FadD26, which also loads them onto PpsA. PpsA then extends them using a malonyl-CoA extender unit. The PpsB protein adds the next malonyl-CoA extender unit. The absence of a dehydratase and an enoyl reductase domains in the PpsA and PpsB modules results in the formation of the diol portion of the phthiocerol moiety. PpsC adds a third malonyl unit (releasing a water molecule due to its dehydratase domain), PpsD adds an (R)-methylmalonyl unit, releasing a water molecule, and PpsE adds a second (R)-methylmalonyl unit, without releasing a water molecule. The incorporation of the methylmalonyl units results in formation of two branched methyl groups in the elongated product. The enzyme does not contain a thioesterase domain [2], and release of the products requires the tesA-encoded type II thioesterase [1].
1.  Rao, A. and Ranganathan, A. Interaction studies on proteins encoded by the phthiocerol dimycocerosate locus of Mycobacterium tuberculosis. Mol. Genet. Genomics 272 (2004) 571–579. [PMID: 15668773]
2.  Trivedi, O.A., Arora, P., Vats, A., Ansari, M.Z., Tickoo, R., Sridharan, V., Mohanty, D. and Gokhale, R.S. Dissecting the mechanism and assembly of a complex virulence mycobacterial lipid. Mol. Cell 17 (2005) 631–643. [PMID: 15749014]
[EC created 2019]

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