Multiple Mechanosensitive Ion Channels from Escherichia coli, Activated at Different Thresholds of Applied Pressure

Abstract

Mechanosensitive ion channels from Escherichia coli were studied in giant proteoliposomes reconstituted from an inner membrane fraction, or in giant round cells in which the outer membrane and the cell wall had been disrupted by a lysozyme-EDTA treatment and a mild osmotic shock. Patch-clamp experiments revealed the presence in these two preparations of an array of different conductances (100 to 2,300 pS in 0.1 M KCl) activated by stretch. The electrical activity induced by stretch in the native membrane was complex, due to the activation of several different conductances. In contrast, patches of proteoliposomes generally contained clusters of identical conductances, which differed from patch to patch. These experiments are consistent with the notion that these different conductances correspond to different proteins in the plasma membrane of E. coli, which segregate into clusters of identical channels on dilution involved in reconstitution in proteoliposomes. These conductances could be grouped into three subfamilies of poorly selective channels. In both preparations, the higher the conductance, the higher was the negative pressure needed for activation. We discuss the putative role of these channels as parts of a multicomponent osmoregulatory system.

Molecular and electrophysiological characterization of a mechanosensitive channel expressed in the chloroplasts of Chlamydomonas

“…However, the possibility that the 0.4-nS conductance is due to proteins intrinsic to E. coli cannot be excluded. It has previously been shown that MscM, which was obtained via reconstitution of proteoliposomes from an inner membrane fraction of E. coli, exhibits a conductance of 0.1-0.15 nS in 0.1 M KCl solution (17). This conductance is comparable to 0.4 nS in a 0.2 M KCl solution, as was used here.…”

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

“…It is widely accepted that mammalian cell volume regulation is governed by ion channels and transporters in the plasma membrane that are responsible for the fluxes of K + and Cl − as well as Ca 2 + (see Okada et al 28 ). This is also true for bacterial cells 5 . By contrast, our study has shown that Msy1 and Msy2 are localized in organellar membranes: Msy1 is localized mainly in the perinuclear ER and Msy2 in the cortical ER.…”

“…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 .…”

YbdG in Escherichia coli is a threshold-setting mechanosensitive channel with MscM activity

“…Martinac and colleagues discovered that hypoosmotic shock could be mimicked by application of slight pressure (0.1-0.3 atm) across an isolated bacterial membrane patch, leading to increased transmembrane electrical current (5). Subsequently, multiple MS conductances, activated at different pressure thresholds, were identified after solubilization of membrane fractions and reconstitution of protein into artificial lipid bilayers (6,7).…”

“…Members of these families can be found in Bacteria, many Archaea, some plants, fungi, and oomycetes (10-12) but are best studied in E. coli (13)(14)(15). Another channel activity, mechanosensitive channel of miniconductance (MscM), is occasionally observed in patch-clamp recordings (6), but the corresponding gene is not known. This channel has a low conductance (∼0.375 nS) but exhibits long-lived open states in response to increased tension.…”