Abstract
The cell membrane provides a functional link between the external environment and the replicating DNA genome by using ligand-gated receptors and chemical signals to activate signaling transduction pathways. However, increasing evidence has also indicated that the phospholipid bilayer itself by altering various physical parameters serves as a sensor that regulate membrane proteins in a specific manner. Changes in thickness and/or curvature of the membrane have been shown to be induced by mechanical forces and transmitted through the transmembrane helices of several types of mechanosensitive (MS) ion channels underlying functions such as osmoregulation in bacteria and sensory processing in mammalian cells. This review focus on recent protein functional and structural data indicating that the activation of bacterial and yeast osmosensors is consistent with thickness-induced tilting changes of the transmembrane domains of these proteins. Membrane thinning in combination with curvature changes may also lead to the lateral transfer of the small lipid-anchored GTPases Ras1 and H-Ras out of lipid rafts for clustering and signaling. The modulation of signaling pathways by amphiphilic peptides and the membrane-active antibiotics colistin and Amphotericin B is also discussed.
Highlights
The emergence of the cell as a functional unity enclosed in a semipermeable lipid bilayer is often associated with the existence of a higher osmotic pressure at the cell interior than at the external environment due to the presence of impermeant intracellular metabolites
When MscL channels are incorporated into lipid bilayers with shorter lipid hydrocarbon chains, the ion channels gate at Osmosensors and Ras Signaling Activation a lower membrane tension whereas the closed state is stabilized by increased thickness (Perozo et al, 2002)
Cdc24 acts as a GEF for Cdc42, a Rho-like GTPase, which is a central switch in the activation of over 20 effector proteins involved in different cellular functions (Phillips et al, 2008), including those responsible of the membrane-protective effects of the cell wall integrity (CWI) pathway (Maeng et al, 2010) as well as in cytokinesis and the organization of the septin proteins responsible of bud morphogenesis (Ballou et al, 2013)
Summary
The emergence of the cell as a functional unity enclosed in a semipermeable lipid bilayer is often associated with the existence of a higher osmotic pressure at the cell interior than at the external environment due to the presence of impermeant intracellular metabolites This gradient of osmotic pressure is one of the most important mechanical forces acting on cell membranes, as it exerts a lateral tension that stretches the lipid bilayer and produce a thickness reduction (Anishkin et al, 2014). Osmotic forces have been demonstrated to activate ion channels such as those formed by the antifungal polyene antibiotic Amphotericin B (AmB) (Ruckwardt et al, 1998) This is due to the rigid 24 Å length structure of the AmB molecule that is unable to span lipid bilayers with a thickness greater than the length of the AmB molecule (Cohen, 2016). It has been estimated that when the in the open state the lipid bilayer
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