Key Laboratory for Biomedical Effects of Nanomaterials & Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, PR China.
Chembiochem. 2012 Apr 16;13(6):862-71. doi: 10.1002/cbic.201200051.
Chain elongation and cyclization of precursors of dihydroxyphenylacetyl-CoA (DPA-CoA) catalyzed by the bacterial type III polyketide synthase DpgA were studied. Two labile intermediates, di- and tri-ketidyl-CoA (DK- and TK-CoA), were proposed and chemically synthesized. In the presence of DpgABD, each of these with [(13)C(3)]malonyl-CoA (MA-CoA) was able to form partially (13)C-enriched DPA-CoA. By NMR and MS analysis, the distribution of (13)C atoms in the partially (13)C-enriched DPA-CoA shed light on how the polyketide chain elongates and cyclizes in the DpgA-catalyzed reaction. Polyketone intermediates elongate in a manner different from that which had been believed: two molecules of DK-CoA, or one DK-CoA plus one acetoacetyl-CoA (AA-CoA), but not two molecules of AA-CoA can form one molecule of DPA-CoA. As a result, polyketidyl-CoA serves as both the starter and extender, whereas polyketone-CoA without the terminal carboxyl group can only act as an extender. The terminal carboxyl group is crucial for the cyclization that likely takes place on CoA.
研究了细菌型 III 聚酮合酶 DpgA 催化的二羟苯乙酰辅酶 A（DPA-CoA）前体的链延伸和环化。提出并化学合成了两种不稳定的中间体，二酮基和三酮基-CoA（DK-CoA 和 TK-CoA）。在 DpgABD 的存在下，这些中间体中的每一个都能与 [(13)C(3)]丙二酰辅酶 A（MA-CoA）形成部分（13)C 标记的 DPA-CoA。通过 NMR 和 MS 分析，部分（13)C 标记的 DPA-CoA 中（13)C 原子的分布揭示了多酮链在 DpgA 催化反应中如何延伸和环化。多酮中间体的延伸方式与以前认为的不同：两个 DK-CoA 分子，或一个 DK-CoA 加一个乙酰乙酰辅酶 A（AA-CoA），而不是两个 AA-CoA 分子可以形成一个 DPA-CoA 分子。因此，多酮酰基-CoA 既是起始物又是延伸物，而没有末端羧基的多酮-CoA 只能作为延伸物。末端羧基对于可能在 CoA 上发生的环化至关重要。
