Thermodynamic evidence of non-muscle myosin II-lipid-membrane interaction.
ABSTRACT A unique feature of protein networks in living cells is that they can generate their own force. Proteins such as non-muscle myosin II are an integral part of the cytoskeleton and have the capacity to convert the energy of ATP hydrolysis into directional movement. Non-muscle myosin II can move actin filaments against each other, and depending on the orientation of the filaments and the way in which they are linked together, it can produce contraction, bending, extension, and stiffening. Our measurements with differential scanning calorimetry showed that non-muscle myosin II inserts into negatively charged phospholipid membranes. Using lipid vesicles made of DMPG/DMPC at a molar ratio of 1:1 at 10mg/ml in the presence of different non-muscle myosin II concentrations showed a variation of the main phase transition of the lipid vesicle at around 23 degrees C. With increasing concentrations of non-muscle myosin II the thermotropic properties of the lipid vesicle changed, which is indicative of protein-lipid interaction/insertion. We hypothesize that myosin tail binds to acidic phospholipids through an electrostatic interaction using the basic side groups of positive residues; the flexible, amphipathic helix then may partially penetrate into the bilayer to form an anchor. Using the stopped-flow method, we determined the binding affinity of non-muscle myosin II when anchored to lipid vesicles with actin, which was similar to a pure actin-non-muscle myosin II system. Insertion of myosin tail into the hydrophobic region of lipid membranes, a model known as the lever arm mechanism, might explain how its interaction with actin generates cellular movement.
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ABSTRACT: A recent report in BMC Cell Biology examines how the balance of extracellular forces and intracellular contractions regulate the shape changes required for oligodendrocyte myelination. A failure of remyelination such as seen in multiple sclerosis could be caused by loss of this balance.Journal of Biology 09/2009; 8(8):78.
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ABSTRACT: The focal adhesion protein vinculin has been implicated in associating with soluble and membranous phospholipids. Here, we investigated the intermolecular interactions of two vinculin tail domains with membrane phospholipids. Previous studies have shown that the tail's unstructured C-terminus affects the mechanical behavior of cells, but not the H3 region. The aim of this work was to establish whether the C-terminal or the H3 region either associate favorably with or anchor in lipid membranes. This work characterizes the energetics and dynamics of phospholipid interactions using differential scanning calorimetry (DSC) as well as circular dichroism (CD) spectroscopy. Biochemical data from tryptophan quenching and SDS-PAGE experiments support calorimetric and CD spectroscopic findings insofar that only vinculin's C-terminus inserts into lipid membranes. These in vitro results provide further insight into the mechanical behavior of vinculin tail regions in cells and contribute to the understanding of their structure and function.Biochemical and Biophysical Research Communications 07/2010; 398(3):433-7. · 2.48 Impact Factor