News extra credit must be from an article that was published within the seven day period prior to the day the article was turned in. ![]() News articles are due via this online form by Friday afternoons at 3:30. You may submit up to two articles per week with a maximum of 100 points per semester. Each science news submission is worth five Above and Beyond class work points. The researchers believe these study insights should also be helpful in understanding and ultimately treating disorders caused by actin dysfunction.įunding was provided by the National Institutes of Health (R01 GM073791, F31 HL156431).As an " Above and Beyond" activity, you can read and respond to a current events science news story. Results from this study provide crucial mechanistic details for a deeper understanding of actin biology as a whole. These are the two proteins found at the ends of the filament in skeletal and cardiac muscles, playing an essential role in the stabilization of actin filaments in muscle fibers, and, without these proteins, our muscles would fall apart. The data also detailed the structural changes induced by two actin filament-capping proteins, CapZ at the barbed end and tropomodulin at the pointed end. These revealed a "flat" actin shape, or conformation, at the uncapped barbed end, versus a "twisted" conformation at the uncapped pointed end. By doing so, they identified hundreds of thousands of filament end views, allowing them to obtain near-atomic scale reconstructions. With artificial intelligence (AI) assistance, the researchers were able to focus on the ends of the filaments instead of their middle, as had previously been the norm in similar research. With this high-resolution imaging technique, a researcher obtains many thousands of snapshots of a target molecule, aligns them computationally, and then averages them to reduce random image "noise" - yielding a 3-D reconstruction of the molecule that may be sharp enough to visualize individual atoms. ![]() In their study, the researchers, including two Penn students - Peter Carman, PhD, a recent graduate student in Dominguez's lab, and Kyle Barrie, PhD, a graduate student currently in the lab, who served as co-first authors - analyzed actin filaments using cryo-EM. But the structural details determining the specificity of these interactions - the details that explain why these two ends function so differently - have been murky. Many other proteins also bind to the barbed and pointed ends of the actin filament. Actin filaments can be stabilized by distinct so-called "capping" proteins that bind to the filament ends to stop further addition or loss of individual actin proteins. The dynamics of actin filaments are governed largely by the "treadmilling" process, through which individual actin proteins are shed from one filament end, known as the pointed end, and added at the other, barbed end. "The results of our study provide a mechanistic understanding of a process we have known about for more than 40 years, referred to as filament treadmilling, and impacts how we view the cellular roles of actin in health and disease," said the study senior author Roberto Dominguez, PhD, the William Maul Measey Presidential Professor of Physiology at Penn. Actin filaments also are major elements in muscle fibers. Rapid changes in actin filaments underlie key cellular events such as movement along surfaces, cell-to-cell contact, and cell division. ![]() It serves as the building-block for long, thin structures called filaments, which provide key structural support as part of the cell "cytoskeleton," the system that gives cells their shape and polarity. Actin is the most abundant protein inside the cells of higher organisms, such as animals.
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