Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK.
Microbiology (Reading). 2023 Jul;169(7). doi: 10.1099/mic.0.001360.
The exchange of ammonium across cellular membranes is a fundamental process in all domains of life. In plants, bacteria and fungi, ammonium represents a vital source of nitrogen, which is scavenged from the external environment. In contrast, in animal cells ammonium is a cytotoxic metabolic waste product and must be excreted to prevent cell death. Transport of ammonium is facilitated by the ubiquitous Amt/Mep/Rh transporter superfamily. In addition to their function as transporters, Amt/Mep/Rh proteins play roles in a diverse array of biological processes and human physiopathology. Despite this clear physiological importance and medical relevance, the molecular mechanism of Amt/Mep/Rh proteins has remained elusive. Crystal structures of bacterial Amt/Rh proteins suggest electroneutral transport, whilst functional evidence supports an electrogenic mechanism. Here, focusing on bacterial members of the family, we summarize the structure of Amt/Rh proteins and what three decades of research tells us concerning the general mechanisms of ammonium translocation, in particular the possibility that the transport mechanism might differ in various members of the Amt/Mep/Rh superfamily.
铵跨细胞膜的交换是所有生命领域的基本过程。在植物、细菌和真菌中，铵代表了一种重要的氮源，它是从外部环境中获取的。相比之下，在动物细胞中，铵是一种细胞毒性代谢废物，必须排泄出去，以防止细胞死亡。铵的运输是由普遍存在的 Amt/Mep/Rh 转运蛋白超家族来完成的。除了作为转运蛋白的功能外，Amt/Mep/Rh 蛋白在各种生物过程和人类病理生理学中发挥作用。尽管具有明显的生理重要性和医学相关性，但 Amt/Mep/Rh 蛋白的分子机制仍然难以捉摸。细菌 Amt/Rh 蛋白的晶体结构表明其为电中性转运，而功能证据支持电致动机制。在这里，我们主要关注家族中的细菌成员，总结了 Amt/Rh 蛋白的结构以及三十年来的研究告诉我们的关于铵转运的一般机制，特别是在 Amt/Mep/Rh 超家族的不同成员中，转运机制可能存在差异的可能性。
