Similar insights, Skiniotis says, will come from applying the same idea to protein structures. They showed, for the first time, that all four of the animal’s hooves leave the ground at once - something that the human eye could not distinguish. In the 1870s, photographer Eadweard Muybridge used high-speed photography technology, which was cutting edge at the time, to capture a series of still images of a galloping horse. To underscore the power of cryo-EM, Skiniotis and others like to draw a comparison with one of the first motion pictures ever made. “The big picture is to move away, as much as possible, from this single, static snapshot,” says Georgios Skiniotis, a structural biologist at Stanford University in California, whose team used the technique to record the activation of a type of cell-signalling molecule called a G-protein-coupled receptor (GPCR) 4. First, myosin becomes cocked or primed, then it attaches to actin and its lever arm swings in working stroke of about 34 nanometres. Researchers have been able to capture images of individual myosin molecules as they move along an actin filament, confirming key details of the motion. Other researchers are focusing their new-found director’s eye on understanding cell-signalling systems, including those underlying opioid overdoses, the gene-editing juggernaut CRISPR–Cas9 and other molecular machines that have been mostly studied with highly detailed, yet static structural maps. Yet it confirmed a decades-old theory and settled debates over the order of the steps in myosin’s choreography. Muench and his colleagues’ myosin movie isn’t feature-length it consists of just two frames showing different stages of the molecular motion. That technology - called time-resolved cryo-electron microscopy (cryo-EM) - now has structural biologists thinking like cinematographers, turning still snapshots of life’s molecular machinery into motion pictures that reveal how it works. “These are experiments that people wanted to do 40 years ago, but they just never had the technology.” “It’s one of the things in the textbook you sort of gloss over,” says Stephen Muench, a structural biologist at the University of Leeds, UK, who co-led the study. ‘The entire protein universe’: AI predicts shape of nearly every known protein In a preprint published in January 3, researchers used a cutting-edge structural biology technique to record this moment, which lasts just milliseconds in living cells. The only hitch is that scientists had never seen this fleeting pre-stroke state - until now. Researchers think that myosin generates force by cocking back the long lever-like arm that is attached to the motor portion of the protein. The basics were first explained in a pair of landmark papers in Nature 1, 2, and they have been confirmed and elaborated on by detailed molecular maps of myosin and its partners. The protein at the centre of the action is myosin, a molecular motor that ratchets itself along rope-like strands of actin proteins - grasping, pulling, releasing and grasping again - to make muscle cells contract. Since the 1950s, scientists have had a pretty good idea of how muscles work.
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