( Scientists exploring the physics of hea...)Scientists identify molecular cause for one form of deafness

Within the cochlea of the inner ear, sound waves cause the basilar membrane to vibrate. These vibrations stimulate hair cells, which then trigger nerve impulses that are transmitted to the brain.

Researchers have now learned that mutations in a protein called espin can cause floppiness in tiny bundles of protein filaments within the hair cells, impairing the passage of vibrations and resulting in deafness.

Filamentous actin (F-actin) is a rod-like protein that provides structural framework in living cells. F-actin is organized into bundles by espin, a linker protein found in sensory cells, including cochlear hair cells. Genetic mutations in espin's F-actin binding sites are linked to deafness in mice and humans.

"We found the structure of the bundles changes dramatically when normal espin is replaced with espin mutants that cause deafness," said Gerard Wong, a professor of materials science and engineering, of physics, and of bioengineering at the University of Illinois at Urbana-Champaign.

"The interior structure of the bundles changes from a rigid, hexagonal array of uniformly twisted filaments, to a liquid crystalline arrangement of filaments," Wong said. "Because the new organization causes the bundles to be more than a thousand times floppier, they cannot respond to sound in the same way. The rigidity of these bundles is essential for hearing."

Wong and his co-authors ?Illinois postdoctoral research associate Kirstin Purdy and Northwestern University professor of cell and molecular biology James R. Bartles ?report their findings in a paper accepted for publication in the journal Physical Review Letters, and posted on its Web site.

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Source:University of Illinois at Urbana-Champaign