Similar to harmonin (USH1C) and whirlin (USH2D), full-length PDZD7 contains three PDZ domains, a harmonin-N like (HNL) domain, and a proline-rich (PR) region.
Moreover, PDZD7 was also shown to interact with USH1 proteins MYO7A (USH1B), harmonin (USH1C), and SANS (USH1G) [18, 24, 25].
At present, only a few PDZD7-binding proteins have been reported, including usherin, ADGRV1, whirlin, harmonin, SANS, and MYO7A [17, 18, 21-25].
Zwaenepoel et al., "A defect in harmonin, a PDZ domain-containing protein expressed in the inner ear sensory hair cells, underlies Usher syndrome type 1C," Nature Genetics, vol.
Masmoudi et al., "Usher syndrome type I G (USH1G) is caused by mutations in the gene encoding SANS, a protein that associates with the USH1C protein, harmonin," Human Molecular Genetics, vol.
The study indicated that the protein called harmonin, which is known to be involved in sound sensing in the inner ear, may also play a role in the transmission of sound information to the brain.
Harmonin is thought to mediate this movement, which then activates the cells and initiates transmission of sound information as electrical and chemical signals to the brain.
"Now we have found a new role for harmonin at the opposite end of these sound-sensing inner hair cells where it appears to control the signal output of the cell," added Lee.
Lee and colleagues, including UI postdoctoral fellows Frederick Gregory, Ph.D., and Keith Bryan, Ph.D., found that harmonin is important for regulating the number of calcium channels present at the sound-transmitting synapse of inner hair cells.
"Harmonin appears to precisely control how many channels are available," Lee said.
The intracellular domain of this variant is able to bind to the PDZ module-containing proteins harmonin and whirlin, which are proposed to anchor usherin to the actin-based cytoskeleton via myosin VII (Adato et al, 2005a).
There is some evidence that the intracellular domain of mammalian usherin interacts with the PDZ-containing proteins harmonin and whirlin, which are proposed to act as a link between usherin and microfilaments (Adato et al., 2005b).