School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
Biochemistry. 2010 Mar 16;49(10):2186-93. doi: 10.1021/bi902176v.
Acyl (peptidyl) carrier protein (ACP or PCP) is a crucial component involved in the transfer of thiol ester-bound intermediates during the biosynthesis of primary and secondary metabolites such as fatty acids, polyketides, and nonribosomal peptides. Although many carrier protein three-dimensional structures have been determined, to date there is no model available for a fungal type I polyketide synthase ACP. Here we report the solution structure of the norsolorinic acid synthase (NSAS) holo ACP domain that has been excised from the full-length multifunctional enzyme. NSAS ACP shows similarities in three-dimensional structure with other type I and type II ACPs, consisting of a four-helix bundle with helices I, II, and IV arranged in parallel. The N-terminus of helix III, however, is unusually hydrophobic, and Phe1768 and Leu1770 pack well with the core of the protein. The result is that unlike other carrier proteins, helix III lies almost perpendicular to the three major helices. Helix III is well-defined by numerous NMR-derived distance restraints and may be less flexible than counterparts in type II FAS and PKS ACPs. When the holo ACP is derivatized with a hexanoyl group, only minor changes are observed between the HSQC spectra of the two ACP species and no NOEs are observed for this hydrophobic acyl group. Along with the mammalian type I FAS, this further strengthens the view that type I ACPs do not show any significant affinity for hydrophobic (nonpolar) chain assembly intermediates attached via the 4'-phosphopantetheine prosthetic group.
酰基（肽基）载体蛋白（ACP 或 PCP）是参与初级和次级代谢物生物合成中硫酯结合中间体转移的关键组成部分，如脂肪酸、聚酮和非核糖体肽。尽管已经确定了许多载体蛋白的三维结构，但迄今为止，还没有真菌 I 型聚酮合酶 ACP 的模型可用。在这里，我们报告了从全长多功能酶中切除的诺索罗林酸合酶（NSAS）全酶 ACP 结构域的溶液结构。NSAS ACP 在三维结构上与其他 I 型和 II 型 ACP 相似，由一个四螺旋束组成，螺旋 I、II 和 IV 平行排列。然而，螺旋 III 的 N 端异常疏水，并且 Phe1768 和 Leu1770 与蛋白质的核心结合良好。结果是，与其他载体蛋白不同，螺旋 III 几乎垂直于三个主要螺旋。螺旋 III 通过大量 NMR 衍生的距离约束得到很好的定义，并且可能比 II 型 FAS 和 PKS ACP 中的对应物更不灵活。当全酶 ACP 用己酰基衍生化时，两种 ACP 物种的 HSQC 谱之间仅观察到微小变化，并且对于该疏水性酰基没有观察到 NOE。与哺乳动物 I 型 FAS 一起，这进一步证实了 I 型 ACP 对通过 4'-磷酸泛酰巯基乙胺辅基连接的非疏水（非极性）链组装中间体没有任何显著亲和力的观点。
