A new group of eubacterial light-driven retinal-binding proton pumps with an unusual cytoplasmic proton donor
A new group of eubacterial light-driven retinal-binding proton pumps with an unusual cytoplasmic proton donor
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DOI：
10.1016/j.bbabio.2015.08.003
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发表时间：
2015-12-01
影响因子：
4.3
通讯作者：
Brown, Leonid S.
中科院分区：
文献类型：
--
作者：
Harris, Andrew;Ljumovic, Milena;Brown, Leonid S.
微生物紫红质的主要功能之一是向外驱动质子在质膜上的传输，它可以提供替代呼吸和叶绿素光合作用的能量来源。质子泵视紫红质存在于古生菌（盐细菌）、多种细菌、许多真菌和一些微观藻类中。绝大多数质子泵具有共同的转运机制，其中来自视网膜希夫碱的质子首先被转移到视网膜细胞外一侧的主要质子受体（通常是Asp）。其次，细胞质侧的席夫碱的再增殖是由羧基质子供体（Asp或Glu）介导的，它位于螺旋C上，通常与螺旋b上的Thr或Ser形成氢键。唯一值得注意的例外是最近在Exiguobacterium中发现的羧基质子供体被赖氨酸取代。在这里，我们描述了一组新的高效的蛋白质细菌视网膜结合光驱动质子泵，它们在螺旋C上缺乏羧基质子供体（通常被Gly取代），但在螺旋b上具有独特的His残基。我们对该基团进行了光谱表征，并提出该组氨酸形成了一个质子供体复合物，补偿了羧基质子供体的损失。(C) 2015 Elsevier B.V.版权所有
One of the main functions of microbial rhodopsins is outward-directed light-driven proton transport across the plasma membrane, which can provide sources of energy alternative to respiration and chlorophyll photosynthesis. Proton-pumping rhodopsins are found in Archaea (Halobacteria), multiple groups of Bacteria, numerous fungi, and some microscopic algae. An overwhelming majority of these proton pumps share the common transport mechanism, in which a proton from the retinal Schiff base is first transferred to the primary proton acceptor (normally an Asp) on the extracellular side of retinal. Next, reprotonation of the Schiff base from the cytoplasmic side is mediated by a carboxylic proton donor (Asp or Glu), which is located on helix C and is usually hydrogen-bonded to Thr or Ser on helix B. The only notable exception from this trend was recently found in Exiguobacterium, where the carboxylic proton donor is replaced by Lys. Here we describe a new group of efficient proteobacterial retinal-binding light-driven proton pumps which lack the carboxylic proton donor on helix C (most often replaced by Gly) but possess a unique His residue on helix B. We characterize the group spectroscopically and propose that this histidine forms a proton-donating complex compensating for the loss of the carboxylic proton donor. (C) 2015 Elsevier B.V. All rights reserved.