Protection of Escherichia coli cells against extreme turgor by activation of MscS and MscL mechanosensitive channels: identification of genes required for MscS activity

Abstract

N.Levina, S.Tötemeyer and N.R.Stokes contributed equally to this workMechanosensitive channels are ubiquitous amongst bacterial cells and have been proposed to have major roles in the adaptation to osmotic stress, in particular in the management of transitions from high to low osmolarity environments. Electrophysiological measurements have identified multiple channels in Escherichia coli cells. One gene, mscL, encoding a large conductance channel has previously been described, but null mutants were without well-defined phenotypes. Here, we report the characterization of a new gene family required for MscS function, YggB and KefA, which has enabled a rigorous test of the role of the channels. The channel determined by KefA does not appear to have a major role in managing the transition from high to low osmolarity. In contrast, analysis of mutants of E.coli lacking YggB and MscL shows that mechanosensitive channels are designed to open at a pressure change just below that which would cause cell disruption leading to death.

Spectator no more, the role of the membrane in regulating ion channel function

“…In bacteria, the opening of the channels occurs at defined pressures and allows the rapid efflux of ions, solute and small molecules reducing the turgor pressure, thus protecting the cell against hypo-osmotic shock [11]. The increased turgor pressure manifests itself as lateral tension within the bilayer and it is for this reason the proteins are also known as stretch channels (Fig 1a).…”

Organellar mechanosensitive channels in fission yeast regulate the hypo-osmotic shock response

“…msy1 -msy2 -undergoes osmotic stress-induced cell death. Upon hypo-osmotic shock, mammalian cells undergo osmotic stress-induced death, such as necrosis 28 , whereas prokaryotic cells experience cell lysis 6 . Thus, to examine whether the decreased viability of msy2 -cells and msy1 -msy2 -cells is due to osmoticinduced cell death or cell lysis, we performed a time-lapse imaging analysis with cells that express EGFP to monitor cell lysis.…”

“…By contrast, the hypo-osmotic shock response in bacterial cells is conducted exclusively by mechanosensitive channels and does not require such a secondary messenger system. In Escherichia coli, three discrete types of mechanosensitive channels, MscM, MscS and MscL, are activated by cell swelling, and release ions and small osmolytes nonselectively to reduce the intracellular osmolarity 5,6 . Genes encoding MscS homologues have been found in the genomes of prokaryotes and cell-walled eukaryotes, (for example, plants, algae and fungi) 7 .…”

“…Genes encoding MscS homologues have been found in the genomes of prokaryotes and cell-walled eukaryotes, (for example, plants, algae and fungi) 7 . While MscS is required for the osmotic response in bacteria 6,8,9 , it is unknown whether eukaryotic MscS homologues are involved in the osmotic response. Rather, eukaryotic MscS homologues analyzed so far, such as Arabidopsis thaliana MscS-like proteins MSL2 and MSL3 and Chlamydomonas reinhardtii MscS homologue MSC1, are associated with chloroplast organization 10,11 .…”

The transient receptor potential channel on the yeast vacuole is mechanosensitive

“…Among Trp-family channels, Osm9 (5), no mechanoreceptor potential C (nompC) (6), stretch inhibitable channel (SIC) (7), polycystin-2 (PC2) (8), and vanilloid receptor-related osmotically activated channel (VR-OAC) (9) are associated with mechanosensitivity in different animals. In prokaryotes, the MS channels MscL and MscS have been cloned, expressed, and crystallized (10)(11)(12)(13). Because they maintain full mechanosensitivity in lipid bilayers and their activities are readily registered by patch-clamp, they have become biophysical models with which to examine the transduction between force and conformation changes (14)(15)(16).…”