Pennisi Rosa, Salvi Daniele, Brandi Valentina, Angelini Riccardo, Ascenzi Paolo, Polticelli Fabio
Department of Sciences, Roma Tre University, Viale Guglielmo Marconi 446, 00146, Rome, Italy.
CIBIO-InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Campus Agrário de Vairão, 4485-661, Vairão, Portugal.
J Mol Evol. 2016 May;82(4-5):207-18. doi: 10.1007/s00239-016-9738-8. Epub 2016 Apr 18.
Alternative oxidases (AOXs) are mitochondrial cyanide-resistant membrane-bound metallo-proteins catalyzing the oxidation of ubiquinol and the reduction of oxygen to water bypassing two sites of proton pumping, thus dissipating a major part of redox energy into heat. Here, the structure of Arabidopsis thaliana AOX 1A has been modeled using the crystal structure of Trypanosoma brucei AOX as a template. Analysis of this model and multiple sequence alignment of members of the AOX family from all kingdoms of Life indicate that AOXs display a high degree of conservation of the catalytic core, which is formed by a four-α-helix bundle, hosting the di-iron catalytic site, and is flanked by two additional α-helices anchoring the protein to the membrane. Plant AOXs display a peculiar covalent dimerization mode due to the conservation in the N-terminal region of a Cys residue forming the inter-monomer disulfide bond. The multiple sequence alignment has also been used to infer a phylogenetic tree of AOXs whose analysis shows a polyphyletic origin for the AOXs found in Fungi and a monophyletic origin of the AOXs of Eubacteria, Mycetozoa, Euglenozoa, Metazoa, and Land Plants. This suggests that AOXs evolved from a common ancestral protein in each of these kingdoms. Within the Plant AOX clade, the AOXs of monocotyledon plants form two distinct clades which have unresolved relationships relative to the monophyletic clade of the AOXs of dicotyledonous plants. This reflects the sequence divergence of the N-terminal region, probably due to a low selective pressure for sequence conservation linked to the covalent homo-dimerization mode.
交替氧化酶（AOXs）是线粒体中对氰化物有抗性的膜结合金属蛋白，催化泛醇氧化并将氧气还原为水，绕过两个质子泵位点，从而将大部分氧化还原能量以热的形式耗散。在此，以布氏锥虫AOX的晶体结构为模板，对拟南芥AOX 1A的结构进行了建模。对该模型的分析以及来自所有生命王国的AOX家族成员的多序列比对表明，AOXs的催化核心具有高度保守性，该催化核心由一个四α螺旋束形成，容纳双铁催化位点，并由另外两个将蛋白质锚定在膜上的α螺旋侧翼包围。由于在形成单体间二硫键的半胱氨酸残基的N端区域具有保守性，植物AOXs呈现出一种特殊的共价二聚化模式。多序列比对还被用于推断AOXs的系统发育树，其分析表明，真菌中发现的AOXs具有多系起源，而真细菌、黏菌、眼虫、后生动物和陆地植物的AOXs具有单系起源。这表明AOXs在这些王国中的每一个中都从一个共同的祖先蛋白进化而来。在植物AOX进化枝内，单子叶植物的AOXs形成两个不同的进化枝，它们与双子叶植物AOXs的单系进化枝的关系尚未解决。这反映了N端区域的序列差异，可能是由于与共价同型二聚化模式相关的序列保守性的选择压力较低。
