TMC1, LHFPL5, and the mechanotransdution complex in hair cells

The channel that governs mechanotransduction (MT) by hair cells in the inner ear has been studied intensively for 4 decades, but its molecular identity remains enigmatic. Recently, transmembrane channel-like protein 1 (TMC1) and lipoma HMGIC fusion partner-like 5 (LHFPL5) are recognized as two critical components of the mechanotransduction complex in inner-ear hair cells. Our recent work examined the localization, physical and functional interactions, and alternative splicing of TMC1 and LHFPL5 by using multiple approaches, including our newly developed ultrasensitive microbead-based single-molecule pulldown (SiMPull) assay. We demonstrated that LHFPL5 physically interacted with and stabilized TMC1 in both heterologous expression systems and in the soma and hair bundle of hair cells. Moreover, the semi-dominant deafness mutation D572N in human TMC1 (D569N in mouse TMC1) severely disrupted LHFPL5 binding and destabilized TMC1 expression. Thus, our findings reveal previously unrecognized physical and functional interactions of TMC1 and LHFPL5 and provide insights into the molecular mechanism by which the D572N mutation causes deafness. Notably, these findings identify a missing link in the currently known physical organization of the mechanotransduction macromolecular complex. In addition, our findings on the alternative splicing of TMC1 and LHFPL5 genes reveal the potential complexity of the MT-complex composition and provide critical insights for guiding future research on the function, regulation, and trafficking of TMC1, and LHFPL5.