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首页> 外文期刊>Journal of Molecular Biology >Crystal structure of red chlorophyll catabolite reductase: enlargement of the ferredoxin-dependent bilin reductase family.
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Crystal structure of red chlorophyll catabolite reductase: enlargement of the ferredoxin-dependent bilin reductase family.

机译：红色叶绿素分解代谢物还原酶的晶体结构：铁氧还蛋白依赖性的胆红素还原酶家族的扩大。

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摘要

The key steps in the degradation pathway of chlorophylls are the ring-opening reaction catalyzed by pheophorbide a oxygenase and sequential reduction by red chlorophyll catabolite reductase (RCCR). During these steps, chlorophyll catabolites lose their color and phototoxicity. RCCR catalyzes the ferredoxin-dependent reduction of the C20/C1 double bond of red chlorophyll catabolite. RCCR appears to be evolutionarily related to the ferredoxin-dependent bilin reductase (FDBR) family, which synthesizes a variety of phytobilin pigments, on the basis of sequence similarity, ferredoxin dependency, and the common tetrapyrrole skeleton of their substrates. The evidence, however, is not robust; the identity between RCCR and FDBR HY2 from Arabidopsis thaliana is only 15%, and the oligomeric states of these enzymes are different. Here, we report the crystal structure of A. thaliana RCCR at 2.4 A resolution. RCCR forms a homodimer, in which each subunit folds in an alpha/beta/alpha sandwich. The tertiary structure of RCCR is similar to those of FDBRs, strongly supporting that these enzymes evolved from a common ancestor. The two subunits are related by noncrystallographic 2-fold symmetry in which the alpha-helices near the edge of the beta-sheet unique in RCCR participate in intersubunit interaction. The putative RCC-binding site, which was derived by superimposing RCCR onto biliverdin-bound forms of FDBRs, forms an open pocket surrounded by conserved residues among RCCRs. Glu154 and Asp291 of A. thaliana RCCR, which stand opposite each other in the pocket, likely are involved in substrate binding and/or catalysis.
机译：叶绿素降解途径中的关键步骤是脱镁叶绿酸加氧酶催化的开环反应和红色叶绿素分解代谢物还原酶（RCCR）的顺序还原。在这些步骤中，叶绿素分解代谢物会失去颜色和光毒性。 RCCR催化铁氧还蛋白依赖性还原红色叶绿素分解代谢产物的C20 / C1双键。 RCCR似乎与铁氧还蛋白依赖性Bilin还原酶（FDBR）家族进化相关，FDBR家族基于序列相似性，铁氧还蛋白依赖性以及其底物的常见四吡咯骨架，合成了多种植物胆红素色素。但是，证据并不充分。拟南芥的RCCR和FDBR HY2之间的同一性仅为15％，这些酶的低聚状态不同。在这里，我们报告了A. thaliana RCCR在2.4 A分辨率下的晶体结构。 RCCR形成同型二聚体，其中每个亚基都折叠在alpha / beta / alpha三明治中。 RCCR的三级结构与FDBR的三级结构相似，强烈支持这些酶从共同祖先进化而来。这两个亚基通过非晶体2倍对称性关联，其中RCCR中唯一的β-折叠边缘附近的α螺旋参与亚基间的相互作用。推定的RCC结合位点是通过将RCCR叠加在结合双肝素的FDBR上而形成的，形成了一个开放的口袋，被RCCR之间的保守残基包围。拟南芥RCCR的Glu154和Asp291在口袋中彼此相对，可能与底物结合和/或催化有关。

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