Moparthi Vamsi K, Kumar Brijesh, Al-Eryani Yusra, Sperling Eva, Górecki Kamil, Drakenberg Torbjörn, Hägerhäll Cecilia
Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, PO Box 124, S-221 00 Lund, Sweden.
Biochim Biophys Acta. 2014 Jan;1837(1):178-85. doi: 10.1016/j.bbabio.2013.09.012. Epub 2013 Oct 1.
quinone oxidoreductase or complex I is a large membrane bound enzyme complex that has evolved from the combination of smaller functional building blocks. Intermediate size enzyme complexes exist in nature that comprise some, but not all of the protein subunits in full size 14-subunit complex I. The membrane spanning complex I subunits NuoL, NuoM and NuoN are homologous to each other and to two proteins from one particular class of Na(+)/H(+) antiporters, denoted MrpA and MrpD. In complex I, these ion transporter protein subunits are prime candidates for harboring important parts of the proton pumping machinery. Using a model system, consisting of Bacillus subtilis MrpA and MrpD deletion strains and a low copy expression plasmid, it was recently demonstrated that NuoN can rescue the strain deleted for MrpD but not that deleted for MrpA, whereas the opposite tendency was seen for NuoL. This demonstrated that the MrpA-type and MrpD-type proteins have unique functional specializations. In this work, the corresponding antiporter-like protein subunits from the smaller enzymes evolutionarily related to complex I were tested in the same model system. The subunits from 11-subunit complex I from Bacillus cereus behaved essentially as those from full size complex I, corroborating that this enzyme should be regarded as a bona fide complex I. The hydrogenase-3 and hydrogenase-4 antiporter-like proteins on the other hand, could substitute equally well for MrpA or MrpD at pH7.4, suggesting that these enzymes have intermediate forms of the antiporter-like proteins, which seemingly lack the functional specificity.
醌氧化还原酶或复合体I是一种大型膜结合酶复合体，由较小的功能性结构单元组合进化而来。自然界中存在中等大小的酶复合体，它们包含了全尺寸14亚基复合体I中的一些但不是全部蛋白质亚基。跨膜的复合体I亚基NuoL、NuoM和NuoN彼此同源，并且与一类特定的Na(+)/H(+)反向转运蛋白中的两种蛋白质同源，分别为MrpA和MrpD。在复合体I中，这些离子转运蛋白亚基是质子泵浦机制重要部分的主要候选者。最近，利用一个由枯草芽孢杆菌MrpA和MrpD缺失菌株以及一个低拷贝表达质粒组成的模型系统，证明了NuoN可以拯救MrpD缺失的菌株，但不能拯救MrpA缺失的菌株，而NuoL的情况则相反。这表明MrpA型和MrpD型蛋白具有独特的功能特化。在这项工作中，在同一模型系统中测试了与复合体I进化相关的较小酶的相应反向转运蛋白样亚基。蜡样芽孢杆菌11亚基复合体I的亚基表现与全尺寸复合体I的亚基基本相同，证实该酶应被视为真正的复合体I。另一方面，氢化酶-3和氢化酶-4反向转运蛋白样蛋白在pH7.4时对MrpA或MrpD的替代效果相同，表明这些酶具有反向转运蛋白样蛋白的中间形式，似乎缺乏功能特异性。
