Role of Tyr residues on the protein surface of cationic cell-wall-peroxidase (CWPO-C) from poplar: Potential oxidation sites for oxidative polymerization of lignin
Role of Tyr residues on the protein surface of cationic cell-wall-peroxidase (CWPO-C) from poplar: Potential oxidation sites for oxidative polymerization of lignin
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DOI：
10.1016/j.phytochem.2007.08.020
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发表时间：
2008-01-01
期刊：
影响因子：
3.8
通讯作者：
Kondo, Ryuichiro
中科院分区：
文献类型：
--
作者：
Sasaki, Shinya;Nonaka, Daisuke;Kondo, Ryuichiro
此前有报道称，与其他植物过氧化物酶不同，来自杨愈伤组织的一种独特的过氧化物酶同工酶——阳离子细胞壁结合过氧化物酶（CWPO-C）可以氧化芥子醇、铁细胞色素c和合成木质素聚合物。在这里，利用化学修饰和同源建模研究了 CWPO-C 的催化机制。模拟的CWPO-C结构预测CWPO-C的血红素口袋的入口与其他植物过氧化物酶的入口大小相同，这表明亚铁细胞色素c和合成木质素聚合物不能与CWPO-C的血红素相互作用。由于 Trp 和 Tyr 残基具有氧化还原活性，因此预计位于蛋白质表面的此类残基是 CWPO-C 的活性位点。 CWPO-C Trp 残基的修饰并未抑制其对愈创木酚和丁香醛连氮的氧化活性。另一方面，使用四硝基甲烷对CWPO-C Tyr残基进行修饰，分别强烈抑制了其对丁香醛连氮和2,6-二甲氧基苯酚的氧化活性，并且还较小程度地抑制了其愈创木酚氧化活性。 Tyr 修饰的 CWPO-C 不会氧化铁细胞色素 c。这些结果表明CWPO-C中的Tyr残基介导其对紫丁香基化合物和高分子量底物的氧化。同源模型表明Tyr-177和Tyr-74位于血红素附近并暴露在CWPO-C的蛋白质表面。这些结果表明，蛋白质表面的 Tyr 残基被认为对于具有多种底物的 CWPO-C 的氧化活性非常重要，并且是植物过氧化物酶家族潜在的独特氧化位点。 (C) 2007 Elsevier Ltd. 保留所有权利。
It was previously reported that an unique peroxidase isoenzyme, cationic cell-wall-bound peroxidase (CWPO-C), from poplar callus oxidizes sinapyl alcohol, ferrocytochrome c and synthetic lignin polymers, unlike other plant peroxidases. Here, the catalytic mechanism of CWPO-C was investigated using chemical modification and homology modeling. The simulated CWPO-C structure predicts that the entrance to the heme pocket of CWPO-C is the same size as those of other plant peroxidases, suggesting that ferrocytochrome c and synthetic lignin polymers cannot interact with the heme of CWPO-C. Since Trp and Tyr residues are redox-active, such residues located on the protein surface were predicted to be active sites for CWPO-C. Modification of CWPO-C Trp residues did not suppress its oxidation activities toward guaiacol and syringaldazine. On the other hand, modification of CWPO-C Tyr residues using tetranitromethane strongly suppressed its oxidation activities toward syringaldazine and 2,6-dimethoxyphenol by 90%, respectively, and also suppressed its guaiacol oxidation activity to a lesser extent. Ferrocytochrome c was not oxidized by Tyr-modified CWPO-C. These results indicate that the Tyr residues in CWPO-C mediate its oxidation of syringyl compounds and high-molecular-weight substrates. Homology modeling indicates that Tyr-177 and Tyr-74 are located near the heme and exposed on the protein surface of CWPO-C. These results suggest that Tyr residues on the protein surface are considered to be important for the oxidation activities of CWPO-C with a wide range of substrates, and potentially unique oxidation sites for the plant peroxidase family. (C) 2007 Elsevier Ltd. All rights reserved.