OSU researchers take step toward gene therapy for deaf patients

SAN FRANCISCO, Sept. 18 (Xinhua) -- By developing a way to better study a large protein essential for hearing and finding a truncated version of it, researchers at Oregon State University (OSU) have taken a step toward gene therapy for deaf patients.

While mutations in the protein, known as otoferlin, are linked to severe congenital hearing loss, a common type of deafness in which patients can hear almost nothing, the research suggests that otoferlin, which is in the cochlea of the inner ear, acts as a calcium-sensitive linker protein.

Published recently in the Proceedings of the National Academy of Sciences, or PNAS, the study also shows that a mutation in otoferlin weakens the binding between the protein and a calcium synapse in the ear, and deficiencies in that interaction might be at the root of hearing loss related to otoferlin, which is difficult to study due to the size of its molecule.

As they try to explore how otoferlin works differently than another neuronal calcium sensor in the brain, synaptotagmin, the researchers in OSU's College of Science developed a single-molecule colocalization binding titration assay for quantitatively probing otoferlin.

"Otoferlin seems only to have one purpose and that is to encode sound in the sensory hair cells in the inner ear," corresponding author Colin Johnson, associate professor of biochemistry and biophysics, explained in a news release from OSU Monday. "And small mutations in otoferlin render people profoundly deaf."

The work by Johnson and his collaborators provides a molecular-level explanation for the observation that otoferlin and synaptotagmin don't have the same functional role. Performed using recombinant protein from cell lysate isolated in vitro, it also validates a methodology for characterizing large, multivalent membrane proteins in general.

"The otoferlin gene is really big, and it makes a huge protein," Johnson said. "The traditional method for making a recombinant protein is using E. coli, but they loathe big proteins." While there is a size limit in terms of what can be packaged into the gene delivery vehicle, the researchers tried to shorten the gene, to find a truncated form that can be used for gene therapy.

"That's the holy grail, trying to find a miniature version of otoferlin that can be packaged into the delivery vehicle and then hopefully the patient can start hearing," he noted. As a result, the team identified a truncated form of otoferlin that can function in the encoding of sound.