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Mutations in Myosin-1c cause Hearing Loss

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We can speak after we can hear. All the rhythms and harmonies of this world are heard by the minute molecular motors in hair cells of our inner ear and perceived by the brain. A tiny imbalance may render someone deaf for life. Scientists from the University Of Pennsylvania School Of Medicine have now identified an amino acid that can disrupt the normal physiology of hearing. This amino acid brings about changes by altering a molecular motor protein residing in the cochlea of inner ear; myosin-1c.

This particular mutation called R156W was identified in a patient who was suffering from cochlear hearing loss. This mutation affects the functioning of protein myosin-1c and its interaction with actin filaments which also play a crucial role in the sensory apparatus of the inner ear. The interplay of actin filaments and myosin-1c is necessary for the normal functioning of the ear. In case, this interaction is disrupted and hearing loss occurs, as has been previously determined.

Scientists at UPenn have now succeeded in studying the mechanical and biochemical properties of this myosin-1c protein that mutates to cause hearing loss. They compared the normal type of the protein with the mutant R156W with respect to their protein kinetics and motility and found that the mutant R156W has a lesser sensitivity to mechanical burden and also exhibits a lower duty ratio. This led to the conclusion that this mutated protein myosin-1c spends lesser time connected to actin filaments than it should under normal circumstances.

Although, it is now a known fact that a mutation in myosin-1c causes hearing loss; the mechanism and reason for it is still unknown. A clear picture of the larger role of myosin-1c is still not available even though its role in important processes of the cell has been discovered, like its involvement in hearing and insulin related glucose uptake within cells. The defects caused by the aforementioned mutation of R156W must be understood in detail to better understand how to prevent its effects and to prevent the associated hearing loss.

Among the many proteins of the myosin family, R156 is one of the most conserved residues. The mutation of R156 affects largely the strain sensitivity and duty ratios. Since this affects the most conserved residue, the probability of other members of myosin family being affected is relatively higher. Professor Michael Greenberg of Pennsylvania University explained that a greater insight into the mechanism of myosin strain sensitivity and its role in mechanotransduction would be of great help in solving the puzzle of hearing loss due to mutations.

National Institute of Health and American Heart Association sponsored this study conducted by the scientists of Pennsylvania University.

Michael J. Greenberg, Tianming Lin, Jeffrey R. Moore, E. Michael Ostap. A HEARING-LOSS ASSOCIATED MYO1C MUTATION (R156W) DECREASES THE MYOSIN DUTY RATIO AND FORCE SENSITIVITY, Unconventional Myosins, 55th Annual Meetinng, Biophysical Society, 3/6/2011
published: 30 Nov 2011 (11:04)

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