20 Azotobacter vinelandiiのフェノール性脂質の生合成(口頭発表の部)

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Alkylresorcinols and alkylpyrones, which have a polar aromatic ring and a hydrophobic alkyl chain, are phenolic lipids found in plants, fungi, and bacteria. In the Gram-negative bacterium Azotobacter vinelandii, phenolic lipids in the membrane of dormant cysts are essential for encystment. We report here an ars operon in A. vinelandii that is responsible for the biosynthesis of the alkylresorcinols in the cysts. The ars operon consisted of four genes, two of which encoded a type III polyketide synthase (PKS), ArsB and ArsC, and another two of which encoded a type I fatty acid synthase (FAS), ArsA and ArsD. In vitro experiments revealed that ArsB and ArsC were an alkylresorcinol synthase and an alkylpyrone synthase, respectively. In vivo and in vitro reconstitution of phenolic lipid synthesis systems with the Ars enzymes suggested that the C22-C26 fatty acids produced by ArsA and ArsD remained attached to the ACP domain of ArsA and were transferred hand-to-hand to the active-site cysteine residues of ArsB and ArsC. The phenolic lipids in A. vinelandii were thus found to be synthesized solely from malonyl-CoA by the four members of the ars operon. This is the first demonstration that a type I FAS interacts directly with a type III PKS through substrate transfer. The importance of the alkylresorcinols for encystment was confirmed by gene inactivation experiments; the lack of alkylresorcinols synthesis caused by ars mutations resulted in the formation of severely impaired cysts, as observed by electron microscopy.
天然有機化合物討論会の論文
2008-09-01

20 Azotobacter vinelandiiのフェノール性脂質の生合成(口頭発表の部)

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