Mitch Leslie writes:

Mice put human runners to shame. Despite taking puny strides, the rodents can log 10 kilometers or more per night on an exercise wheel. But the mice that muscle biologist Eric Olson of the University of Texas Southwestern Medical Center in Dallas and colleagues unveiled in 2015 stood out. On a treadmill, the mice could scurry up a steep 10% grade for about 90 minutes before faltering, 31% longer than other rodents. Those iron mice differed from counterparts in just one small way—the researchers had genetically altered the animals to lack one muscle protein. That was enough to unleash superior muscle performance. “It’s like you’ve taken the brakes off,” Olson says.

Just as startling was the nature of the crucial protein. Muscles house some gargantuan proteins. Dystrophin, a structural protein whose gene can carry mutations that cause muscular dystrophy, has more than 3600 amino acids. Titin, which acts like a spring to give muscles elasticity, is the biggest known protein, with more than 34,000 amino acids. The protein disabled in the mice has a paltry 46. Although researchers have probed how muscles work for more than 150 years, they had completely missed the huge impact this tiny protein, called myoregulin, has on muscle function.

Olson and his colleagues weren’t the only ones to be blindsided by Lilliputian proteins. As scientists now realize, their initial rules for analyzing genomes discriminated against identifying those pint-size molecules. Now, broader criteria and better detection methods are uncovering minuscule proteins by the thousands, not just in mice, but in many other species, including humans. “For the first time, we are about to explore this universe of new proteins,” says biochemist Jonathan Weissman of the University of California, San Francisco.

Biologists are just beginning to delve into the functions of those molecules, called microproteins, micropeptides, or miniproteins. But their small size seems to allow them to jam the intricate workings of larger proteins, inhibiting some cellular processes while unleashing others. Early findings suggest microproteins bolster the immune system, control destruction of faulty RNA molecules, protect bacteria from heat and cold, dictate when plants flower, and provide the toxic punch for many types of venom. “There’s probably going to be small [proteins] involved in all biological processes. We just haven’t looked for them before,” says biochemist Alan Saghatelian of the Salk Institute for Biological Studies in San Diego, California. [Continue reading…]