Heteromultimerization of Prokaryotic Bacterial Cyclic Nucleotide-Gated (bCNG) Ion Channels, Members of the Mechanosensitive Channel of Small Conductance (MscS) Superfamily

Novel MscL agonists that allow multiple antibiotics cytoplasmic access activate the channel through a common binding site

The antibiotic resistance crisis is becoming dire, yet in the past several years few potential antibiotics or adjuvants with novel modes of action have been identified. The bacterial mechanosensitive channel of large conductance, MscL, found in the majority of bacterial species, including pathogens, normally functions as an emergency release valve, sensing membrane tension upon low-osmotic stress and discharging cytoplasmic solutes before cell lysis. Opening the huge ~30Å diameter pore of MscL inappropriately is detrimental to the cell, allowing solutes from and even passage of drugs into to cytoplasm. Thus, MscL is a potential novel drug target. However, there are no known natural agonists, and small compounds that modulate MscL activity are just now being identified. Here we describe a small compound, K05, that specifically modulates MscL activity and we compare results with those obtained for the recently characterized MscL agonist 011A. While the structure of K05 only vaguely resembles 011A, many of the findings, including the binding pocket, are similar. On the other hand, both in vivo and molecular dynamic simulations indicate that the two compounds modulate MscL activity in significantly different ways.

Characterizing the mechanosensitive response of Paraburkholderia graminis membranes

Bacterial mechanosensitive channels gate in response to membrane tension, driven by shifts in environmental osmolarity. The mechanosensitive channels of small conductance (MscS) and large conductance (MscL) from Escherichia coli (Ec) gate in response to mechanical force applied to the membrane. Ec-MscS is the foundational member of the MscS superfamily of ion channels, a diverse family with at least fifteen subfamilies identified by homology to the pore lining helix of Ec-MscS, as well as significant diversity on the N- and C-termini. The MscL family of channels are homologous to Ec-MscL. In a rhizosphere associated bacterium, Paraburkholderia graminis C4D1M, mechanosensitive channels are essential for cell survival during changing osmotic environments such as a rainstorm. Utilizing bioinformatics, we predicted six MscS superfamily members and a single MscL homologue. The MscS superfamily members fall into at least three subfamilies: bacterial cyclic nucleotide gated, multi-TM, and extended N-terminus. Osmotic downshock experiments show that wildtype P. graminis cells contain a survival mechanism that prevents cell lysis in response to hypoosmotic shock. To determine if this rescue is due to mechanosensitive channels, we developed a method to create giant spheroplasts of P. graminis to explore the single channel response to applied mechanical tension. Patch clamp electrophysiology on these spheroplasts shows two unique conductances: MscL-like and MscS-like. These conductances are due to likely three unique proteins. This indicates that channels that gate in response to mechanical tension are present in the membrane. Here, we report the first single channel evidence of mechanosensitive ion channels from P. graminis membranes.