The spring in the unicellular Vorticella is a contractile fiber bundle, called the spasmoneme, which runs the length of the stalk. At rest, the stalk is elongated like a stretched telephone cord. When it contracts, the spasmoneme winds back in a flash, forming a tight coil. To find out how fast and how hard Vorticella recoils, France and colleagues used modern microscopes and tools to measure the force and speed of the spring. This is one powerful engine, France reports. The spasmoneme's contraction is measured in nano-newtons of force and centimeters/second of speed in a biological world where the ruler markings are usually in tiny pico-newtons and micrometers/second. Gram for gram, the power of the spasmoneme engine outperforms human muscles and car engines.
It also runs on a different fuel. Molecular motors that power muscle contraction, for example, use ATP molecules for energy. The spasmoneme runs on calcium, but its drive mechanism was poorly understood until France and colleagues got under the nano hood. Like van Leeuwenhoek, the researchers studied Vorticella under the microscope but they also had specialized biochemical methods to slow and inhibit the contraction, to freeze-frame it, and to discern details of the calcium fuel system.
Earlier research had identified a cellular protein, spasmin, as the possible calcium-responsive component of the stalk. "The Vorticella spasmins are now known to belong to the centrin family of calcium-binding proteins," says France. "Centrins are ubiquitous to eukaryotic cells and some family members are found in filamentous structures in organisms other than Vorticella, ranging from green algae to humans."
In sorting out centrin's role in the Vorticella spring, France and colleagues found that an antibody to Vorticella centrin abolished contractility. Along with other evidence, this interference suggests that the spasmoneme uses a powerful centrin-based mechanism that is unlike any complex actin or microtubule-based cellular engine, says France. "This leads us closer to understanding two things: how cells use centrin-based engines to generate enormous forces and how we can possibly reconstruct centrin-based materials and devices for our own use at the micrometer and nanometer scales."
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