Three Routes To Modulate the Pore Size of the MscL Channel/Nanovalve

Abstract

MscL is a bacterial mechanosensitive channel that protects cells from lysis upon acute decrease in external osmotic environment. It is one of the best characterized mechanosensors known, thus serving as a paradigm of how such molecules sense and respond to stimuli. In addition, the fact that it can be genetically modified, expressed, isolated, and manipulated has led to its proposed use as a triggered nanovalve for various functions including sensors within microelectronic array chips, as well as vesicular-based targeted drug release. X-ray crystallography reveals a homo-pentameric complex with each subunit containing two transmembrane α-helices (TM1 and TM2) and a single carboxyl terminal α-helix arranging within the complex to form a five-fold cytoplasmic bundle (CB), whose function and stability remain unclear. In this study, we show three routes that throttle the open channel conductance. When the linker between the TM2 and CB domain is shortened by deletions or constrained by either cross linking or heavy metal coordination, the conductance of the channel is reduced; in later two cases, even reversibly. While having implications for the stability of the CB, these data also provide routes for engineering MscL sensors that are more versatile for potential nanotech devices.

The MscS and MscL Families of Mechanosensitive Channels Act as Microbial Emergency Release Valves

“…This stabilizer is sometimes called a "slide helix" or "anchor" and is seen in several channels, suggesting a more conserved function (37). Although initially controversial (2,87), it now appears that the C-terminal bundle remains intact in the open structure, with the TM2-to-bundle linker creating five portals that can act as potential molecular sieves (85), while the TM2 cytoplasmic interface appears to be dynamic and enters the membrane during the gating process (35).…”

“…Indeed, the observation that a charge within the MscL pore can gate the channel has led to the engineering of nanopores that are actuated by light (43) and pH (42). We can now not only change the modality of MscL but also control the compounds that may pass through it (84), as well as reversibly modulate the pore size (85). Such channels may someday be utilized in a variety of nanodevices, including targeted drug delivery systems.…”

Bacterial Mechanosensitive Channels: Models for Studying Mechanosensory Transduction

“…Electron microscopy studies, along with the observed ability of MscL to let molecules as large as insulin pass through the pore, suggest that the C-terminal domain might dissociate and incorporate into the transmembrane domain during channel opening (151, 167). At odds with this, however, are MD simulations and mutational analyses, which suggest that the C-terminal domain remains intact and undergoes only minor dissociation proximal to the TM2 helix (31,40,52,146,162).…”

Biophysical and Structural Studies of Escherichia coli Mechanosensitive Channel of Large Conductance in Lipid Bilayers

“…The light-induced channel opening system previously described, for example, introduced charges to the channel pore, which would select against certain like-charged molecules as demonstrated in a separate experiment . An alternative approach is to use the cytoplasmic domain as a molecular size-based sieve, based on the observation that the dissociation of the domain is at least not necessary (if it happens at all) (L. M. Yang & Blount, 2011;L. M. Yang et al, 2012).…”

“…Finally, interest in MscL has increased in recent years because of its demonstrated potential to be modified and implemented as a stimulus-triggered nanovalve in liposomal drug delivery systems (A. Foo et al, 2015;Kocer et al, 2007;L. M. Yang et al, 2012) and for introducing cell-impermeable biomarkers and bioactive molecules into mammalian cells (Doerner et al, 2012).…”