Life's dynamic proteins (Introduction)

by David Turell @, Thursday, January 07, 2016, 14:26 (3242 days ago)

If one takes different active proteins from living matter, they come together to move in patterns:-http://www.nature.com/news/the-physics-of-life-1.19105?WT.ec_id=NATURE-20160107&spMailingID=50403822&spUserID=MjA1NjAyNzAyOQS2&spJobID=840817500&spReportId=ODQwODE3NTAwS0#/ref-link-13-"First, Zvonimir Dogic and his students took microtubules — threadlike proteins that make up part of the cell's internal 'cytoskeleton' — and mixed them with kinesins, motor proteins that travel along these threads like trains on a track. Then the researchers suspended droplets of this cocktail in oil and supplied it with the molecular fuel known as adenosine triphosphate (ATP).-"To the team's surprise and delight, the molecules organized themselves into large-scale patterns that swirled on each droplet's surface. Bundles of microtubules linked by the proteins moved together “like a person crowd-surfing at a concert”, says Dogic.-***- "Bausch led one of the first precise, quantitative experiments. He and his colleagues mixed actin, a filament that forms most of the cytoskeleton of complex cells, with myosin, a molecular motor that 'walks' on actin and makes muscles contract. The researchers added myosin's natural fuel, ATP, then put the mixture on a microscope slide and watched. “We didn't do anything; we just added the stuff,” Bausch says. At low concentrations, the actin filaments swam around without recognizable order. But at higher densities, they formed pulsating clusters, swirls and bands. Bausch and his colleagues immediately recognized and quantified phase transitions of the kind that Vicsek and others had predicted. Their 2010 paper5 helped to ignite the experimental active-matter field.-"Among the studies that followed were Dogic's 2012 microtubule experiments1, which used another walking protein, kinesin. The resulting patterns were much more complex and dynamic than the ones Bausch saw: the flowing microtubules looked like fingerprint whorls in motion. Dogic and his team also noticed that the orderly alignment of this flow would occasionally break down and produce 'defects': discontinuities in the pattern that resemble converging longitude lines at the North and South poles. These defects were dynamic, moving around like self-propelled particles.-***-"Active matter excites scientists because it so closely resembles the most complex self-organizing systems known: living organisms. In 2011, Dogic and his colleagues reported9 that microtubule bundles anchored at one end to air bubbles on a microscope slide beat in synchronized, wave-like patterns eerily reminiscent of the hair-like cilia and flagella that protrude from the surfaces of some cells. And in his 2012 paper1, he noted a striking similarity between his microtubule flows and cytoplasmic streaming, a process in which cytoskeletal filaments team up to whisk a cell's contents around like “a giant washing machine”, he says.-"To probe whether active-matter theory can reveal biological mechanisms, Daniel Needleman, a biophysicist at Harvard University in Cambridge, Massachusetts, studied the spindle: a microtubule-based structure that controls the separation of chromosomes during cell division. He wanted to test the idea, suggested by earlier theories and experiments, that short-range microtubule-kinesin interactions by themselves were sufficient to yield spindle-like structures. He first used sophisticated microscopes to examine extracts from frog egg cells, quantifying microtubule density, orientation and stresses during spindle formation. “It really was not clear at all until Dan came along that you could measure all these things,” says Howard.-"Needleman then merged his measurements with models of how active matter self-organizes. In 2014, he and Jan Brugués, a biologist at the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden, Germany, reported that, consistent with theory, the interactions they observed among closely spaced microtubules are enough to produce the spindle and keep it stable10. “People have argued that you need more complex processes,” says Needleman. “But the fact that one can understand so much of the spindle without invoking any of that shows that it's certainly not necessary.”-Comment: A clue as to how life works. These active protein molecules from living matter, self-organize to a degree. Again the question, how did chance evolution find such special proteins from the billions of potential proteins that can be conceivably made?


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