Abe Masato, Murai Masatoshi, Ichimaru Naoya, Kenmochi Atsushi, Yoshida Takehiko, Kubo Akina, Kimura Yuka, Moroda Aki, Makabe Hidefumi, Nishioka Takaaki, Miyoshi Hideto
Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Biochemistry. 2005 Nov 15;44(45):14898-906. doi: 10.1021/bi051568t.
Studies on the inhibitory mechanism of acetogenins, the most potent inhibitors of mitochondrial complex I (NADH-ubiquinone oxidoreductase), are useful for elucidating the structural and functional features of the terminal electron transfer step of this enzyme. Previous studies of the structure-activity relationship revealed that except for the alkyl spacer linking the two toxophores (i.e., the hydroxylated THF and the gamma-lactone rings), none of the multiple functional groups of these inhibitors is essential for potent inhibition. To elucidate the function of the alkyl spacer, two sets of systematically selected analogues were synthesized. First, the length of the spacer was varied widely. Second, the local flexibility of the spacer was specifically reduced by introducing multiple bond(s) into different regions of the spacer. The optimal length of the spacer for inhibition was approximately 13 carbon atoms. The decrease in the strength of the inhibitory effect caused by elongating the spacer from 13 carbons was much more drastic than that caused by shortening. Local flexibility in a specific region of the spacer was not important for the inhibition. These observations indicate that the active conformation of the spacer is not an extended form, and is not necessarily restricted to a certain rigid shape. Moreover, an analogue in which a spacer covering 10 carbon atoms was hardened into a rodlike shape still maintained a potent inhibitory effect. Our results strongly suggest that the spacer portion is free from steric congestion arising from the putative binding site probably because there is no cavity-like binding site for the spacer portion. The manner of acetogenin binding to the enzyme may not be explained by a simple "key and keyhole" analogy.
对线粒体复合物I（NADH - 泛醌氧化还原酶）最有效的抑制剂——产乙酸素抑制机制的研究，有助于阐明该酶末端电子传递步骤的结构和功能特征。先前对构效关系的研究表明，除了连接两个毒基团（即羟基化四氢呋喃和γ - 内酯环）的烷基间隔基外，这些抑制剂的多个官能团中没有一个对于强效抑制是必不可少的。为了阐明烷基间隔基的功能，合成了两组系统选择的类似物。首先，间隔基的长度有很大变化。其次，通过在间隔基的不同区域引入多重键，特异性地降低了间隔基的局部柔韧性。抑制的最佳间隔基长度约为13个碳原子。将间隔基从13个碳原子延长导致的抑制作用强度下降比缩短间隔基导致的下降要剧烈得多。间隔基特定区域的局部柔韧性对抑制并不重要。这些观察结果表明，间隔基的活性构象不是伸展形式，也不一定局限于某种刚性形状。此外，一个间隔基覆盖10个碳原子并硬化成棒状的类似物仍然保持强效抑制作用。我们的结果强烈表明，间隔基部分可能没有来自假定结合位点的空间拥挤，因为间隔基部分没有类似腔的结合位点。产乙酸素与酶的结合方式可能不能用简单的“钥匙和锁孔”类比来解释。
