Ankyrin repeats of varying lengths appear in more than 400 human proteins expressed in many tissues, Bennett said. For example, ankyrin repeats are found in association with specialized hair cells of the inner ear, where they play a critical role in converting sound (a mechanical stimulus) into an electrical signal that can be transmitted to the brain ?a process known as mechanotransduction.
Ankyrin proteins also coordinate the ion channels and transporters that control the beating of the heart. In 2004, Bennett's team linked mutations in the gene ankyrin-B to an inherited cardiac arrhythmia syndrome that can lead to sudden death (http://www.dukemednews.org/news/article.php?id=9389).
Earlier study of the atomic structure of 12 ankyrin repeats suggested that ankyrin proteins consisting of 24 or more repeats might form a super-helical spiral with spring-like properties, the researchers said.
Using atomic force microscopy (AFM) to view individual molecules in the current study, Marszalek and Pratt research associate Yong Jiang found that ankyrin repeats indeed display a hook-like shape consistent with a spring. AFM is a technique for analyzing the surface of materials all the way down to the level of the atom. Marszalek and Pratt graduate student Gwangrog Lee further examined the molecules' elastic properties by attaching one end of the molecules to a glass slide and gently pulling at the other end with the AFM cantilever.
"After thousands of stretches, a pattern emerged," Marszalek said. "The molecule exhibited linear elasticity--a property that had never been seen in any other protein."