Variable autoinhibition among deafness-associated variants of Diaphanous 1 (DIAPH1)

One of the earliest mapped human deafness genes, DIAPH1 , encodes the formin DIAPH1. To date, at least three distinct mutations in the C-terminal domains and two additional mutations in the N-terminal region are associated with autosomal dominant hearing loss. The underlying molecular mechanisms are not known, and the role of formins in the inner ear is not well understood. In this study we use biochemical assays to test the hypotheses that autoinhibition and/or actin assembly activities are disrupted by DFNA1 mutations. Our results indicate that C-terminal mutant forms of DIAPH1 are functional in vitro and promote actin filament assembly. Similarly, N-terminal mutants are well-folded and have quaternary structures and thermal stabilities similar to the WT protein. The strength of the autoinhibitory interactions varies widely among mutants, with the ttaa , A265S and I530S mutations having an affinity similar to WT and the 1213x and Δ ag mutations completely abolishing autoinhibition. These data indicate that, in some cases, hearing loss may be linked to reduced inhibition of actin assembly.