Programmed Bending Reveals Dynamic Mechanochemical Coupling in Supported Lipid Bilayers

In living cells, mechanochemical coupling represents a dynamic means by which membrane components are spatially organized. An extra-ordinary example of such coupling involves curvature-dependent polar localization of chemically-distinct lipid domains at bacterial poles, which also undergo dramatic reequilibration upon subtle changes in their interfacial environment such as during sporulation. Here, we demonstrate that such interfacially-triggered mechanochemical coupling can be recapitulated in vitro by simultaneous, real-time introduction of mechanically-generated periodic curvatures and attendant strain-induced lateral forces in lipid bilayers supported on elastomeric substrates. In particular, we show that real-time wrinkling of the elastomeric substrate prompts a dynamic domain reorganization within the adhering bilayer, producing large, oriented liquid-ordered domains in regions of low curvature. Our results suggest a mechanism in which interfacial forces generated during surface wrinkling and the topographical deformation of the bilayer combine to facilitate dynamic reequilibration prompting the observed domain reorganization. We anticipate this curvature-generating model system will prove to be a simple and versatile tool for a broad range of studies of curvature-dependent dynamic reorganizations in membranes that are constrained by the interfacial elastic and dynamic frameworks such as the cell wall, glycocalyx, and cytoskeleton

Real-time visualization of heterotrimeric G protein Gq activation in living cells

Contains fulltext : 97296.pdf (publisher's version ) (Open Access)BACKGROUND: Gq is a heterotrimeric G protein that plays an important role in numerous physiological processes. To delineate the molecular mechanisms and kinetics of signalling through this protein, its activation should be measurable in single living cells. Recently, fluorescence resonance energy transfer (FRET) sensors have been developed for this purpose. RESULTS: In this paper, we describe the development of an improved FRET-based Gq activity sensor that consists of a yellow fluorescent protein (YFP)-tagged Ggamma2 subunit and a Galphaq subunit with an inserted monomeric Turquoise (mTurquoise), the best cyan fluorescent protein variant currently available. This sensor enabled us to determine, for the first time, the kon (2/s) of Gq activation. In addition, we found that the guanine nucleotide exchange factor p63RhoGEF has a profound effect on the number of Gq proteins that become active upon stimulation of endogenous histamine H1 receptors. The sensor was also used to measure ligand-independent activation of the histamine H1 receptor (H1R) upon addition of a hypotonic stimulus. CONCLUSIONS: Our observations reveal that the application of a truncated mTurquoise as donor and a YFP-tagged Ggamma2 as acceptor in FRET-based Gq activity sensors substantially improves their dynamic range. This optimization enables the real-time single cell quantification of Gq signalling dynamics, the influence of accessory proteins and allows future drug screening applications by virtue of its sensitivity

Mechanics rules cell biology

Cells in the musculoskeletal system are subjected to various mechanical forces in vivo. Years of research have shown that these mechanical forces, including tension and compression, greatly influence various cellular functions such as gene expression, cell proliferation and differentiation, and secretion of matrix proteins. Cells also use mechanotransduction mechanisms to convert mechanical signals into a cascade of cellular and molecular events. This mini-review provides an overview of cell mechanobiology to highlight the notion that mechanics, mainly in the form of mechanical forces, dictates cell behaviors in terms of both cellular mechanobiological responses and mechanotransduction

The alpha-kinase family: an exceptional branch on the protein kinase tree

The alpha-kinase family represents a class of atypical protein kinases that display little sequence similarity to conventional protein kinases. Early studies on myosin heavy chain kinases in Dictyostelium discoideum revealed their unusual propensity to phosphorylate serine and threonine residues in the context of an alpha-helix. Although recent studies show that some members of this family can also phosphorylate residues in non-helical regions, the name alpha-kinase has remained. During evolution, the alpha-kinase domains combined with many different functional subdomains such as von Willebrand factor-like motifs (vWKa) and even cation channels (TRPM6 and TRPM7). As a result, these kinases are implicated in a large variety of cellular processes such as protein translation, Mg2+ homeostasis, intracellular transport, cell migration, adhesion, and proliferation. Here, we review the current state of knowledge on different members of this kinase family and discuss the potential use of alpha-kinases as drug targets in diseases such as cancer

Femtosecond Dynamics of Solvation: Microscopic Friction and Coherent Motion in Dense Fluids

In this paper, we present detailed experimental and theoretical studies of the femtosecond dynamics of microscopic friction. The real-time rotational motion of a well-defined system of diatomic solute in monatomic solvent has been studied for two solvents ranging from gas to liquid densities. Both coherent inertial and diffusive limits of the motion and all stages in the transition between these two regimes are observed in detail. The transient anisotropies over the entire range of experimental densities and solvents are well-represented by the J-coherence bimolecular collision model presented here. This stochastic hard-sphere collision model explicitly relates the physical properties of the solvent to the anisotropy and the coefficient of rotational friction, permitting calculation of the transient anisotropy from the Enskog hard-sphere collision frequency. Friction coefficients obtained from J-coherence analysis of experimental anisotropies were compared with those from Gordon J-diffusion, and Langevin−Einstein analyses, and with the hydrodynamic range of friction. The density cutoff for applicability of diffusive or continuum treatments is such that the angular trajectory for average J in the angular velocity autocorrelation lifetime is ∼50°, while the microscopic, molecular picture of the friction can be applied from the gas to the liquid

Femtochemistry in Nanocavities: Reactions in Cyclodextrins

We present our first studies of the femtosecond dynamics of reactions in confined nanocavities in water solutions. Intramolecular proton transfer and isomerization dynamics of a hydrogen-bonded molecule (HPMO) in liquid solutions and encapsulated in the cavity formed by β-cyclodextrin (diameter ∼8 Å) is studied using the technique of fluorescence up-conversion. Our results suggest that the proton transfer in aprotic solvents occurs in much less than 300 fs while upon encapsulation this initial step is slowed to the subpicosecond time scale. Furthermore, in these aprotic solvents, HPMO undergoes a picosecond twisting motion around the interaromatic single bond, which is noticeably inhibited when the molecule is inside the nanocavity. Such studies of condensed-phase femtochemistry in nanocavities offer several promising extensions

Femtosecond Dynamics of Solvation: Microscopic Friction and Coherent Motion in Dense Fluids

In this paper, we present detailed experimental and theoretical studies of the femtosecond dynamics of microscopic friction. The real-time rotational motion of a well-defined system of diatomic solute in monatomic solvent has been studied for two solvents ranging from gas to liquid densities. Both coherent inertial and diffusive limits of the motion and all stages in the transition between these two regimes are observed in detail. The transient anisotropies over the entire range of experimental densities and solvents are well-represented by the J-coherence bimolecular collision model presented here. This stochastic hard-sphere collision model explicitly relates the physical properties of the solvent to the anisotropy and the coefficient of rotational friction, permitting calculation of the transient anisotropy from the Enskog hard-sphere collision frequency. Friction coefficients obtained from J-coherence analysis of experimental anisotropies were compared with those from Gordon J-diffusion, and Langevin−Einstein analyses, and with the hydrodynamic range of friction. The density cutoff for applicability of diffusive or continuum treatments is such that the angular trajectory for average J in the angular velocity autocorrelation lifetime is ∼50°, while the microscopic, molecular picture of the friction can be applied from the gas to the liquid