Direct transfer of starter substrates from type I fatty acid synthase to type III polyketide synthases in phenolic lipid synthesis
Direct transfer of starter substrates from type I fatty acid synthase to type III polyketide synthases in phenolic lipid synthesis
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DOI：
10.1073/pnas.0709819105
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发表时间：
2008-01-22
影响因子：
11.1
通讯作者：
Horinouchi, Sueharu
中科院分区：
文献类型：
--
作者：
Miyanaga, Akimasa;Funa, Nobutaka;Horinouchi, Sueharu
烷基间苯二酚和烷基吡喃酮具有极性芳环和疏水烷基链，是在植物、真菌和细菌中发现的酚类脂质。在革兰氏阴性菌棕色固氮菌中，休眠孢囊膜中的酚类脂质是包囊形成所必需的。A. vinelandii由两种III型聚酮酶（PKS）ArsB和ArsC合成，ArsB和ArsC由ars操纵子编码。然而，疏水酰基链的合成细节，这可能是作为起始底物的III型聚酮酶（PKS），是未知的。在这里，我们表明，两个I型脂肪酸脱氢酶（FAS），ArsA和ArsD，这是ars操纵子的成员，负责从丙二酰辅酶A的C-22-C-26脂肪酸的生物合成。在体内和体外重建的酚类脂质合成系统与Ars酶表明，C-22-C-26脂肪酸产生的ArsA和ArsD仍然连接到ACP结构域的ArsA和转移手到手的活性位点半胱氨酸残基的ArsB和ArsC。然后III型PKS使用脂肪酸作为起始底物，并使用丙二酰辅酶A进行两次或三次延伸以产生酚脂质。A.因此发现vinelandii仅通过ars操纵子的四个成员由丙二酰辅酶A合成。这是第一次证明，I型FAS直接与III型PKS通过底物转移相互作用。
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. The aromatic moieties of the phenolic lipids in A. vinelandii are synthesized by two type III polyketide synthases (PKSs), ArsB and ArsC, which are encoded by the ars operon. However, details of the synthesis of hydrophobic acyl chains, which might serve as starter substrates for the type III polyketide synthases (PKSs), were unknown. Here, we show that two type I fatty acid synthases (FASs), ArsA and ArsD, which are members of the ars operon, are responsible for the biosynthesis of C-22-C-26 fatty acids from malonyl-CoA. In vivo and in vitro reconstitution of phenolic lipid synthesis systems with the Ars enzymes suggested that the C-22-C-26 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 type III PKSs then used the fatty acids as starter substrates and carried out two or three extensions with malonyl-CoA to yield the phenolic lipids. 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.