Shimada H, Grutzner J B, Kozlowski J F, McLaughlin J L
Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
Biochemistry. 1998 Jan 20;37(3):854-66. doi: 10.1021/bi972348l.
Certain plant species belonging to the family Annonaceae produce Annonaceous acetogenins, which are a unique class of long-chain fatty acid derivatives with potent cytotoxicity. Putative protein targets of the acetogenins are membrane-associated proteins, including complex I. Asimicin and its analogues constitute a class of Annonaceous acetogenins containing two tetrahydrofuran (THF) rings with hydrocarbon chains tethered to each ring; an alpha,beta-unsaturated gamma-lactone ring is terminal to one of the alkyl chains. The compounds examined in this study differ in the length of the alkyl chain between the THF rings and the lactone ring. The positions of both the THF and the lactone rings within liposomal membranes were determined by proton (1H) nuclear magnetic resonance spectroscopy. The depth of membrane penetration of acetogenins, coupled to membrane diffusion, controls the conformation of acetogenins as they diffuse to an active site. Based on 1H intermolecular nuclear Overhauser effects (NOEs), the THF rings of all acetogenins studied reside near the polar interfacial head group region of the DMPC. This was corroborated by 1H two-dimensional NOE spectroscopy and differential scanning calorimetry studies. The 1H difference NOE spectra indicated that the lactone rings of asimicin and parviflorin, the latter of which has two fewer carbons in its alkyl chain, are located below the glycerol backbone in the membrane. In contrast with asimicin and parviflorin, the lactone ring of longimicin B, an asimicin analogue with an alkyl chain four carbons shorter, resides close to the midplane in the membrane. This was corroborated by manganese-induced broadening studies. Since the THF rings are located near the center of the acetogenin molecules and the lactone ring is terminal to a long alkyl chain, these observations indicate that an asimicin-type acetogenin can be in either sickle-shaped or U-shaped conformations, depending on the length of the alkyl chain between the THF rings and the lactone ring. Interestingly, longimicin B does not exhibit significant cytotoxicity, but parviflorin is as cytotoxic as asimicin. The cytotoxicity of the asimicin-type of acetogenins would seem to be strongly related to the membrane conformation. This is the first report elucidating the conformation of Annonaceous acetogenins in membranes.
番荔枝科的某些植物物种会产生番荔枝乙酰精，它们是一类独特的具有强大细胞毒性的长链脂肪酸衍生物。乙酰精的假定蛋白质靶点是膜相关蛋白，包括复合体I。阿西米辛及其类似物构成了一类番荔枝乙酰精，含有两个四氢呋喃（THF）环，每个环都连接着烃链；一个α,β-不饱和γ-内酯环位于其中一条烷基链的末端。本研究中检测的化合物在THF环和内酯环之间的烷基链长度上有所不同。通过质子（1H）核磁共振光谱确定了脂质体膜内THF环和内酯环的位置。乙酰精与膜扩散相关的膜穿透深度控制着乙酰精扩散到活性位点时的构象。基于1H分子间核Overhauser效应（NOE），所有研究的乙酰精的THF环都位于二肉豆蔻酰磷脂酰胆碱（DMPC）的极性界面头部基团区域附近。这通过1H二维NOE光谱和差示扫描量热法研究得到了证实。1H差异NOE光谱表明，阿西米辛和小花番荔枝素（后者的烷基链中碳原子少两个）的内酯环位于膜中甘油主链下方。与阿西米辛和小花番荔枝素不同，长叶番荔枝素B（一种烷基链短四个碳原子的阿西米辛类似物）的内酯环位于膜的中间平面附近。这通过锰诱导加宽研究得到了证实。由于THF环位于乙酰精分子的中心附近，而内酯环位于长烷基链的末端，这些观察结果表明，阿西米辛型乙酰精可以呈镰刀形或U形构象，这取决于THF环和内酯环之间烷基链的长度。有趣的是，长叶番荔枝素B没有显著的细胞毒性，但小花番荔枝素的细胞毒性与阿西米辛一样强。阿西米辛型乙酰精的细胞毒性似乎与膜构象密切相关。这是第一份阐明番荔枝乙酰精在膜中的构象的报告。
