Concept: Mechanosensitive channels
The activation mode of the mechanosensitive ion channel, MscL, by lysophosphatidylcholine differs from tension-induced gating
- FASEB journal : official publication of the Federation of American Societies for Experimental Biology
- Published almost 4 years ago
One of the best-studied mechanosensitive channels is the mechanosensitive channel of large conductance (MscL). MscL senses tension in the membrane evoked by an osmotic down shock and directly couples it to large conformational changes leading to the opening of the channel. Spectroscopic techniques offer unique possibilities to monitor these conformational changes if it were possible to generate tension in the lipid bilayer, the native environment of MscL, during the measurements. To this end, asymmetric insertion of l-α-lysophosphatidylcholine (LPC) into the lipid bilayer has been effective; however, how LPC activates MscL is not fully understood. Here, the effects of LPC on tension-sensitive mutants of a bacterial MscL and on MscL homologs with different tension sensitivities are reported, leading to the conclusion that the mode of action of LPC is different from that of applied tension. Our results imply that LPC shifts the free energy of gating by interfering with MscL-membrane coupling. Furthermore, we demonstrate that the fine-tuned addition of LPC can be used for controlled activation of MscL in spectroscopic studies.-Mukherjee, N., Jose, M. D., Birkner, J. P., Walko, M., Ingólfsson, H. I., Dimitrova, A., Arnarez, C., Marrink, S. J., Koçer, A. The activation mode of the mechanosensitive ion channel, MscL, by lysophosphatidylcholine differs from tension-induced gating.
When bacteria encounter surfaces, they respond with surface colonization and virulence induction. The mechanisms of bacterial mechanosensation and downstream signaling remain poorly understood. Here, we describe a tactile sensing cascade in Caulobacter crescentus in which the flagellar motor acts as sensor. Surface-induced motor interference stimulated the production of the second messenger cyclic diguanylate by the motor-associated diguanylate cyclase DgcB. This led to the allosteric activation of the glycosyltransferase HfsJ to promote rapid synthesis of a polysaccharide adhesin and surface anchoring. Although the membrane-embedded motor unit was essential for surface sensing, mutants that lack external flagellar structures were hypersensitive to mechanical stimuli. Thus, the bacterial flagellar motor acts as a tetherless sensor reminiscent of mechanosensitive channels.
Mechanosensitive (MS) channels provide protection against hypo-osmotic shock in bacteria whereas eukaryotic MS channels fulfil a multitude of important functions beside osmoregulation. Interactions with the membrane lipids are responsible for the sensing of mechanical force for most known MS channels. It emerged recently that not only prokaryotic, but also eukaryotic, MS channels are able to directly sense the tension in the membrane bilayer without any additional cofactor. If the membrane is solely viewed as a continuous medium with specific anisotropic physical properties, the sensitivity towards tension changes can be explained as result of the hydrophobic coupling between membrane and transmembrane ™ regions of the channel. The increased cross-sectional area of the MS channel in the active conformation and elastic deformations of the membrane close to the channel have been described as important factors. However, recent studies suggest that molecular interactions of lipids with the channels could play an important role in mechanosensation. Pockets in between TM helices were identified in the MS channel of small conductance (MscS) and YnaI that are filled with lipids. Less lipids are present in the open state of MscS than the closed according to MD simulations. Thus it was suggested that exclusion of lipid fatty acyl chains from these pockets, as a consequence of increased tension, would trigger gating. Similarly, in the eukaryotic MS channel TRAAK it was found that a lipid chain blocks the conducting path in the closed state. The role of these specific lipid interactions in mechanosensation are highlighted in this review.
Researchers have discovered a synthetic small molecule that activates a mechanosensitive ion channel involved in a blood disorder.
Sensing and responding to mechanical stimuli is an ancient behavior and ubiquitous to all forms of life. One of its players ‘mechanosensitive ion channels’ are involved in processes from osmosensing in bacteria to pain in humans. However, the mechanism of mechanosensing is yet to be elucidated. This review describes recent developments in the understanding of a bacterial mechanosensitive channel. Force from the lipid principle of mechanosensation, new methods to understand protein-lipid interactions, the role of water in the gating, the use of engineered mechanosensitive channels in the understanding of the gating mechanism and application of the accumulated knowledge in the field of drug delivery, drug design and sensor technologies are discussed.
Immunofluorescence, a powerful technique to detect specific targets using fluorescently labeled antibodies, has been widely used in both scientific research and clinical diagnostics. The probes should be made with small antibodies and high brightness. We conjugated GFP binding protein (GBP) nanobodies, small single-chain antibodies from llamas, with new ~7 nm quantum dots. These provide simple and versatile immunofluorescence nano-probes with nanometer accuracy and resolution. Using the new probes we tracked the walking of individual kinesin motors and measured their 8 nm step sizes; we tracked Piezo1 channels, which are eukaryotic mechanosensitive channels; we also tracked AMPA receptors on living neurons. Finally, we used a new super-resolution algorithm based on blinking of (small) quantum dots that allowed ~ 2 nm precision.
The search for new and effective antimicrobial agents has never been as important; however, since the discovery of antibiotics, exploring the antimicrobial activity of dyes has been forgotten. Antimicrobial dyes are an untapped resource and have the ability to potentially combat the spread of drug-resistant bacteria either alone or as antimicrobial adjuvants. The mechanosensitive ion channel of large conductance (MscL) is highly conserved and ubiquitous in bacterial species. There is evidence to suggest that at least one triphenylmethane dye acts through the highly conserved MscL channel and combining the two approaches of exploring the mechanism of action of other triphenylmethane dyes or antimicrobial dyes in general and the novel MscL target provides a new opportunity for further exploration.