Calisto Filipa, Pereira Manuela M
Instituto de Tecnologia Química e Biológica-António Xavier, Universidade Nova de Lisboa, Oeiras, Portugal.
BioISI-Biosystems & Integrative Sciences Institute, Faculdade de Ciências, Universdade de Lisboa, Lisboa, Portugal.
Front Chem. 2021 Apr 13;9:663706. doi: 10.3389/fchem.2021.663706. eCollection 2021.
Several energy-transducing microbial enzymes have their peripheral subunits connected to the membrane through an integral membrane protein, that interacts with quinones but does not have redox cofactors, the so-called NrfD-like subunit. The periplasmic nitrite reductase (NrfABCD) was the first complex recognized to have a membrane subunit with these characteristics and consequently provided the family's name: NrfD. Sequence analyses indicate that NrfD homologs are present in many diverse enzymes, such as polysulfide reductase (PsrABC), respiratory alternative complex III (ACIII), dimethyl sulfoxide (DMSO) reductase (DmsABC), tetrathionate reductase (TtrABC), sulfur reductase complex (SreABC), sulfite dehydrogenase (SoeABC), quinone reductase complex (QrcABCD), nine-heme cytochrome complex (NhcABCD), group-2 [NiFe] hydrogenase (Hyd-2), dissimilatory sulfite-reductase complex (DsrMKJOP), arsenate reductase (ArrC) and multiheme cytochrome sulfite reductase (MccACD). The molecular structure of ACIII subunit C (ActC) and Psr subunit C (PsrC), NrfD-like subunits, revealed the existence of ion-conducting pathways. We performed thorough primary structural analyses and built structural models of the NrfD-like subunits. We observed that all these subunits are constituted by two structural repeats composed of four-helix bundles, possibly harboring ion-conducting pathways and containing a quinone/quinol binding site. NrfD-like subunits may be the ion-pumping module of several enzymes. Our data impact on the discussion of functional implications of the NrfD-like subunit-containing complexes, namely in their ability to transduce energy.
几种能量转换微生物酶的外周亚基通过一种整合膜蛋白与膜相连，该整合膜蛋白与醌相互作用但没有氧化还原辅因子，即所谓的NrfD样亚基。周质亚硝酸还原酶（NrfABCD）是第一个被认识到具有这种特征的膜亚基的复合物，因此赋予了该家族名称：NrfD。序列分析表明，NrfD同源物存在于许多不同的酶中，如多硫化物还原酶（PsrABC）、呼吸替代复合物III（ACIII）、二甲基亚砜（DMSO）还原酶（DmsABC）、连四硫酸盐还原酶（TtrABC）、硫还原酶复合物（SreABC）、亚硫酸盐脱氢酶（SoeABC）、醌还原酶复合物（QrcABCD）、九血红素细胞色素复合物（NhcABCD）、2型[NiFe]氢化酶（Hyd-2）、异化亚硫酸盐还原酶复合物（DsrMKJOP）、砷酸盐还原酶（ArrC）和多血红素细胞色素亚硫酸盐还原酶（MccACD）。ACIII亚基C（ActC）和Psr亚基C（PsrC）这两种NrfD样亚基的分子结构揭示了离子传导途径的存在。我们进行了全面的一级结构分析，并构建了NrfD样亚基的结构模型。我们观察到，所有这些亚基均由两个由四螺旋束组成的结构重复序列构成，可能含有离子传导途径，并包含一个醌/醌醇结合位点。NrfD样亚基可能是几种酶的离子泵模块。我们的数据影响了对含NrfD样亚基复合物功能意义的讨论，即它们转换能量的能力。
