Fluorescence microscopy of piezo1 in droplet hydrogel bilayers

Fluorescence Approaches for Characterizing Ion Channels in Synthetic Bilayers

Ion channels are membrane proteins that play important roles in a wide range of fundamental cellular processes. Studying membrane proteins at a molecular level becomes challenging in complex cellular environments. Instead, many studies focus on the isolation and reconstitution of the membrane proteins into model lipid membranes. Such simpler, in vitro, systems offer the advantage of control over the membrane and protein composition and the lipid environment. Rhodopsin and rhodopsin-like ion channels are widely studied due to their light-interacting properties and are a natural candidate for investigation with fluorescence methods. Here we review techniques for synthesizing liposomes and for reconstituting membrane proteins into lipid bilayers. We then summarize fluorescence assays which can be used to verify the functionality of reconstituted membrane proteins in synthetic liposomes.

Single-molecule imaging of pore-forming toxin dynamics in droplet interface bilayers

Single-channel recording from pore-forming toxins (PFTs) provides a clear and direct molecular readout of toxin action. However to complete any mechanistic understanding of PFT behavior, this functional kinetic readout must be linked to the underlying changes in toxin structure, binding, conformation, or stoichiometry. Here we review how single-molecule imaging methods might be used to further our understanding of PFTs, and provide detailed practical guidance on the use of droplet interface bilayers as a method capable of examining both single-molecule fluorescence and single-channel electrical signals from PFTs.

In vitro cell stretching technology (IsoStretcher) as an approach to unravel Piezo1-mediated cardiac mechanotransduction

The transformation of electrical signals into mechanical action of the heart underlying blood circulation results in mechanical stimuli during active contraction or passive filling distention, which conversely modulate electrical signals. This feedback mechanism is known as cardiac mechano-electric coupling (MEC). The cardiac MEC involves complex activation of mechanical biosensors initiating short-term and long-term effects through Ca2+ signals in cardiomyocytes in acute and chronic pressure overload scenarios (e.g. cardiac hypertrophy). Although it is largely still unknown how mechanical forces alter cardiac function at the molecular level, mechanosensitive channels, including the recently discovered family of Piezo channels, have been thought to play a major role in the cardiac MEC and are also suspected to contribute to development of cardiac hypertrophy and heart failure. The earliest reports of mechanosensitive channel activity recognized that their gating could be controlled by membrane stretch. In this article, we provide an overview of the stretch devices, which have been employed for studies of the effects of mechanical stimuli on muscle and heart cells. We also describe novel experiments examining the activity of Piezo1 channels under multiaxial stretch applied using polydimethylsiloxane (PDMS) stretch chambers and IsoStretcher technology to achieve isotropic stretching stimulation to cultured HL-1 cardiac muscle cells which express an appreciable amount of Piezo1.

Mechanosensitive Ion Channels: Structural Features Relevant to Mechanotransduction Mechanisms

Activation of mechanosensitive ion channels underlies a variety of fundamental physiological processes that require sensation of mechanical force. Different mechanosensitive channels adapt distinctive structures and mechanotransduction mechanisms to fit their biological roles. How mechanosensitive channels work, especially in animals, has been extensively studied in the past decade. Here we review key findings in the functional and structural characterizations of these channels and highlight the structural features relevant to the mechanotransduction mechanism of each specific channel.

The Fusion of Lipid and DNA Nanotechnology

Lipid membranes form the boundary of many biological compartments, including organelles and cells. Consisting of two leaflets of amphipathic molecules, the bilayer membrane forms an impermeable barrier to ions and small molecules. Controlled transport of molecules across lipid membranes is a fundamental biological process that is facilitated by a diverse range of membrane proteins, including ion-channels and pores. However, biological membranes and their associated proteins are challenging to experimentally characterize. These challenges have motivated recent advances in nanotechnology towards building and manipulating synthetic lipid systems. Liposomes-aqueous droplets enclosed by a bilayer membrane-can be synthesised in vitro and used as a synthetic model for the cell membrane. In DNA nanotechnology, DNA is used as programmable building material for self-assembling biocompatible nanostructures. DNA nanostructures can be functionalised with hydrophobic chemical modifications, which bind to or bridge lipid membranes. Here, we review approaches that combine techniques from lipid and DNA nanotechnology to engineer the topography, permeability, and surface interactions of membranes, and to direct the fusion and formation of liposomes. These approaches have been used to study the properties of membrane proteins, to build biosensors, and as a pathway towards assembling synthetic multicellular systems.

Piezo1 mechanosensitive channels: what are they and why are they important

Mechanosensitive (MS) ion channels are integral membrane proteins which play a crucial role in fast signaling during mechanosensory transduction processes in living cells. They are ubiquitous and old in the evolutionary sense, given their presence in cells from all three kingdoms of life found on Earth, including bacterial, archaeal, and eukaryotic organisms. As molecular transducers of mechanical force, MS channels are activated by mechanical stimuli exerted on cellular membranes, upon which they rapidly and efficiently convert these stimuli into electrical, osmotic, and/or chemical intracellular signals. Most of what we know about the gating mechanisms of MS channels comes from the work carried out on bacterial channels. However, recent progress resulting from identification and structural information of eukaryotic K2P-type TREK and TRAAK as well as Piezo1 and Piezo2 MS channels has greatly contributed to our understanding of the common biophysical principles underlying the gating mechanism and evolutionary origins of these fascinating membrane proteins. Using Piezo1 channels as an example, we briefly describe in this review what we have learned about their biophysics, physiological functions, and potential roles in "mechanopathologies."