PDF(Pubmed)
Abstract：
Chalcone isomerases (CHIs) have well-established roles in the biosynthesis of plant flavonoid metabolites. Saccharomyces cerevisiae possesses two predicted CHI-like proteins, Aim18p (encoded by YHR198C) and Aim46p (YHR199C), but it lacks other enzymes of the flavonoid pathway, suggesting that Aim18p and Aim46p employ the CHI fold for distinct purposes. Here, we demonstrate using proteinase K protection assays, sodium carbonate extractions, and crystallography that Aim18p and Aim46p reside on the mitochondrial inner membrane and adopt CHI folds, but they lack select active site residues and possess an extra fungal-specific loop. Consistent with these differences, Aim18p and Aim46p lack CHI activity and also the fatty acid-binding capabilities of other CHI-like proteins, but instead bind heme. We further show that diverse fungal homologs also bind heme and that Aim18p and Aim46p possess structural homology to a bacterial hemoprotein. Collectively, our work reveals a distinct function and cellular localization for two CHI-like proteins, introduces a new variation of a hemoprotein fold, and suggests that ancestral CHI-like proteins were hemoproteins.
摘要：
查尔酮异构酶（CHIs）在植物类黄酮代谢产物的生物合成中具有公认的作用。酿酒酵母具有两种预测的CHI样蛋白，Aim18p（由YHR198C编码）和Aim46p（YHR199C），但是它缺乏类黄酮途径的其他酶，这表明Aim18p和Aim46p将CHI折叠用于不同的目的。这里,我们证明了使用蛋白酶K保护试验，碳酸钠萃取，和晶体学Aim18p和Aim46p驻留在线粒体内膜上并采用CHI折叠，但它们缺乏选择活性位点残基，并具有额外的真菌特异性环。与这些差异一致，Aim18p和Aim46p缺乏查尔酮异构酶活性以及其他CHI样蛋白的脂肪酸结合能力，而是绑定血红素。我们进一步表明，各种真菌同源物也结合血红素，并且Aim18p和Aim46p与细菌血液蛋白具有结构同源性。总的来说，我们的工作揭示了两种CHI样蛋白的独特功能和细胞定位，引入了血液蛋白折叠的新变化，并表明祖先的CHI样蛋白是血液蛋白。
