YbdG in Escherichia coli is a threshold-setting mechanosensitive channel with MscM activity
YbdG in Escherichia coli is a threshold-setting mechanosensitive channel with MscM activity
复制标题
DOI：
10.1073/pnas.1001405107
复制
发表时间：
2010-07-13
影响因子：
11.1
通讯作者：
Booth, Ian R.
中科院分区：
文献类型：
--
作者：
Schumann, Ulrike;Edwards, Michelle D.;Booth, Ian R.
我们描述了一种机械敏感（MS）通道，它具有微电导（MscM）活动的机械敏感通道，并在门控方面表现出独特的特性。机械敏感通道对膜张力作出反应，从细菌到人类普遍存在，并且在结构和功能上表现出巨大的多样性。这些通道保护细菌和古细菌免受低渗休克，并且是叶绿体形状的关键决定因素。鉴于小电导机械敏感通道 (MscS) 和大电导机械敏感通道 (MscL) 在细菌中发挥的主导作用，在大多数生物体中观察到的多个 MS 通道同系物的作用仍然不清楚。在这里，我们证明MscS同源物YbdG扩大了大肠杆菌细胞可以存活的低渗休克范围，但其表达水平不足以抵御严重休克。 YbdG 蛋白的过度表达提供了完整的保护。渗透压可增强 ybdG 基因的转录和翻译，这与该蛋白在低渗休克生存中的作用一致。通过标准膜片钳方法测量天然通道的电导是不可能的。然而，功能齐全的 YbdG 突变通道 V229A 在膜斑块中表现出与 MScM 活性一致的电导。我们发现，MscM 活性源自不止一种基因产物，因为 ybdG 缺失突变体仍然偶尔表现出类似 MscM 的电导。我们提出ybdG编码低丰度MscM型MS通道，其在细胞中缓解低水平的膜张力，从而无需激活主要的MS通道MscS和MscL。
We describe a mechanosensitive (MS) channel that has mechanosensitive channel of miniconductance (MscM) activity, and displays unique properties with respect to gating. Mechanosensitive channels respond to membrane tension, are ubiquitous from bacteria to man, and exhibit a great diversity in structure and function. These channels protect Bacteria and Archaea against hypoosmotic shock and are critical determinants of shape in chloroplasts. Given the dominant roles played in bacteria by the mechanosensitive channel of small conductance (MscS) and the mechanosensitive channel of large conductance (MscL), the role of the multiple MS channel homologs observed in most organisms remains obscure. Here we demonstrate that a MscS homolog, YbdG, extends the range of hypoosmotic shock that Escherichia coli cells can survive, but its expression level is insufficient to protect against severe shocks. Overexpression of the YbdG protein provides complete protection. Transcription and translation of the ybdG gene are enhanced by osmotic stress consistent with a role for the protein in survival of hypoosmotic shock. Measurement of the conductance of the native channel by standard patch clamp methods was not possible. However, a fully functional YbdG mutant channel, V229A, exhibits a conductance in membrane patches consistent with MscM activity. We find that MscM activities arise from more than one gene product because ybdG deletion mutants still exhibit an occasional MscMlike conductance. We propose that ybdG encodes a low- abundance MscM- type MS channel, which in cells relieves low levels of membrane tension, obviating the need to activate the major MS channels, MscS and MscL.