Relating biochemistry and function in the myosin superfamily

166

137

All cell functions that involve membrane deformation or a change in cell shape (e.g., endocytosis, exocytosis, cell motility, and cytokinesis) are regulated by membrane tension. While molecular contacts between the plasma membrane and the underlying actin cytoskeleton are known to make significant contributions to membrane tension, little is known about the molecules that mediate these interactions. We used an optical trap to directly probe the molecular determinants of membrane tension in isolated organelles and in living cells. Here, we show that class I myosins, a family of membrane-binding, actin-based motor proteins, mediate membrane/cytoskeleton adhesion and thus, make major contributions to membrane tension. These studies show that class I myosins directly control the mechanical properties of the cell membrane; they also position these motor proteins as master regulators of cellular events involving membrane deformation.actin ͉ brush border ͉ cytoskeleton ͉ microvilli ͉ optical trap

Section: Discussionmentioning

confidence: 99%

Control of cell membrane tension by myosin-I

Nambiar

McConnell²,

Tyska³

2009

166

137

“…We note that this is the observed duty ratio at saturating ATP and saturating actin concentrations. The duty ratio is ∼5-10%, which is expected for β-cardiac myosin, as it is a low duty ratio motor (16,17).…”

Section: R453cmentioning

confidence: 99%

Molecular consequences of the R453C hypertrophic cardiomyopathy mutation on human β-cardiac myosin motor function

Sommese

Sung

Nag³

et al. 2013

163

229

Cardiovascular disorders are the leading cause of morbidity and mortality in the developed world, and hypertrophic cardiomyopathy (HCM) is among the most frequently occurring inherited cardiac disorders. HCM is caused by mutations in the genes encoding the fundamental force-generating machinery of the cardiac muscle, including β-cardiac myosin. Here, we present a biomechanical analysis of the HCM-causing mutation, R453C, in the context of human β-cardiac myosin. We found that this mutation causes a ∼30% decrease in the maximum ATPase of the human β-cardiac subfragment 1, the motor domain of myosin, and a similar percent decrease in the in vitro velocity. The major change in the R453C human β-cardiac subfragment 1 is a 50% increase in the intrinsic force of the motor compared with wild type, with no appreciable change in the stroke size, as observed with a dual-beam optical trap. These results predict that the overall force of the ensemble of myosin molecules in the muscle should be higher in the R453C mutant compared with wild type. Loaded in vitro motility assay confirms that the net force in the ensemble is indeed increased. Overall, this study suggests that the R453C mutation should result in a hypercontractile state in the heart muscle.

“…Within the cell, linear motors, including DNA and RNA polymerase, dyneins, kinesins, and myosin, play a critical role in transcription, mitosis, meiosis, muscle contraction, and transporting organelles and synaptic vesicles (1)(2)(3)(4)(5). In eukaryotic mitochondria, a rotary motor, ATP synthase, produces ATP by harnessing the flow of protons down an electrochemical proton gradient (6,7).…”

mentioning

confidence: 99%

Microoxen: Microorganisms to move microscale loads

Weibel

Garstecki²,

Ryan³

et al. 2005

365

291

It is difficult to harness the power generated by biological motors to carry out mechanical work in systems outside the cell. Efforts to capture the mechanical energy of nanomotors ex vivo require in vitro reconstitution of motor proteins and, often, protein engineering. This study presents a method for harnessing the power produced by biological motors that uses intact cells. The unicellular, biflagellated algae Chlamydomonas reinhardtii serve as ''microoxen.'' This method uses surface chemistry to attach loads (1-to 6-m-diameter polystyrene beads) to cells, phototaxis to steer swimming cells, and photochemistry to release loads. These motile microorganisms can transport microscale loads (3-m-diameter beads) at velocities of Ϸ100 -200 m⅐sec ؊1 and over distances as large as 20 cm.biological motors ͉ Chlamydomonas ͉ phototaxis ͉ microfluidics ͉ microspheres T his study demonstrates the biological propulsion of microscale loads by the unicellular photosynthetic algae Chlamydomonas reinhardtii (CR). We exploit the chemistry of the algal cell wall to attach single 1-to 6-m polymer beads to CR. Cells with these ''loads'' attached swim at velocities as high as 100-200 m⅐sec Ϫ1 , approximately the velocity of unmodified cells. CR is phototactic and can be guided by using visible light ( Ϸ 500 nm); we have used this phototaxis to control the transport of microscale loads. A photocleavable linker between the surface of the bead and the cell wall allows us to release loads from the surface of the cell photochemically. We have combined these processes to pick up, transport, guide, and drop off beads by using motile cells.There are many examples of nanometer-scale motors in nature. Within the cell, linear motors, including DNA and RNA polymerase, dyneins, kinesins, and myosin, play a critical role in transcription, mitosis, meiosis, muscle contraction, and transporting organelles and synaptic vesicles (1-5). In eukaryotic mitochondria, a rotary motor, ATP synthase, produces ATP by harnessing the flow of protons down an electrochemical proton gradient (6, 7). Outside of the cell, ciliary dyneins drive the beating of eukaryotic flagella and cilia. In bacteria, a complex of Ϸ20 proteins makes up the remarkable rotary motor that powers the motion of flagella (8).Interest in biological motors is based on both their transduction of energy and their small size and hence their possible relevance to micro͞nanotechnology; the remarkable work of Walker, Vale, Kinosita, Hirokawa, Yanagida and others (9-17) has transformed our understanding of molecular motors. One outcome has been the design and fabrication of new synthetic motors composed entirely of biological molecules (18, 19); another outcome has been the integration of components onto recombinant biological motors (20)(21)(22).Here, we use biological motors intact in cells that use flagella (23). An advantage of this strategy over that using isolated and reconstituted motors is its simplicity. It (i) avoids purification and reconstitution of individual motor proteins, (ii) takes...