Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan.
J Biol Inorg Chem. 2010 Nov;15(8):1331-9. doi: 10.1007/s00775-010-0692-4. Epub 2010 Aug 10.
Cytochrome P450(BSβ), a H(2)O(2)-dependent cytochrome P450 catalyzing the hydroxylation of long-alkyl-chain fatty acids, lacks the general acid-base residue around the heme, which is indispensable for the efficient generation of the active species using H(2)O(2). On the basis of the crystal structure of the palmitic acid bound form of cytochrome P450(BSβ), it was suggested that the role of the general acid-base function was provided by the carboxylate group of fatty acids. The participation of the carboxylate group of the substrate was supported by the fact that cytochrome P450(BSβ) can catalyze oxidations of nonnatural substrates such as styrene and ethylbenzene in the presence of a series of short-alkyl-chain carboxylic acids as a dummy molecule of fatty acid. We refer to a series of short-alkyl-chain carboxylic acids as a "decoy molecule". As shown here, we have clarified the crystal structure of the decoy-molecule-bound form and elucidated that the location of its carboxylate group is virtually the same as that of palmitic acid in the heme cavity, indicating that the carboxylate group of the decoy molecule serves as the general acid-base catalyst. This result further confirms that the role of the acid-base function is satisfied by the carboxylate group of the substrates. In addition, the structure analysis of the substrate-free form has clarified that no remarkable structural change is induced by the binding of the decoy molecule as well as fatty acid. Consequently, whether the carboxylate group is positioned in the active site provides the switching mechanism of the catalytic cycle of cytochrome P450(BSβ).
细胞色素 P450（BSβ）是一种依赖于 H₂O₂的细胞色素 P450，可催化长链脂肪酸的羟化，缺乏血红素周围的一般酸碱残基，这对于使用 H₂O₂高效生成活性物质是必不可少的。基于结合棕榈酸的细胞色素 P450（BSβ）的晶体结构，有人提出，一般酸碱功能的作用是由脂肪酸的羧基基团提供的。底物的羧基基团的参与得到了以下事实的支持：细胞色素 P450（BSβ）可以在一系列短链羧酸作为脂肪酸的虚拟分子的存在下，催化非天然底物如苯乙烯和乙苯的氧化。我们将一系列短链羧酸称为“诱饵分子”。如本文所示，我们已经阐明了诱饵分子结合形式的晶体结构，并阐明了其羧基基团的位置实际上与血红素腔中棕榈酸的位置相同，表明诱饵分子的羧基基团充当一般酸碱催化剂。这一结果进一步证实了酸碱功能的作用是由底物的羧基基团来满足的。此外，对无底物形式的结构分析表明，诱饵分子以及脂肪酸的结合不会引起明显的结构变化。因此，羧基基团是否位于活性部位提供了细胞色素 P450（BSβ）催化循环的切换机制。
