OTOL1

OTOL1 (Otolin-1) is an inner-ear scaffold protein implicated in otoconia/otolith assembly and balance sensing through Ca2+-dependent oligomerization of its C-terminal gC1q domain (PMID:34445792). This domain mediates both Ca2+ binding and trimerization, and natural substitutions at key residues disrupt these properties: R339S, R342W, and R402P destabilize the apo-gC1q domain, with R342W driving aberrant self-aggregation and R402P abolishing trimerization, while Q426R is stabilizing (PMID:34445792). Ca2+ partially rescues the destabilizing effect of R342W and Q426R at higher concentrations but cannot compensate for R402P, which is fully Ca2+-insensitive, establishing these residues as critical determinants of normal gC1q oligomeric assembly and Ca2+ responsiveness (PMID:34445792). Beyond this biophysical characterization of the gC1q domain (PMID:34445792), no further mechanistic detail on OTOL1 has been characterized in the available corpus.

1. 2021 Medium

   It was unknown which molecular features govern Otolin-1 assembly; biophysical dissection of the gC1q domain established that it mediates Ca2+-dependent trimerization and that specific residues control stability, oligomerization, and Ca2+ responsiveness.

   Evidence Structural and biophysical analysis of wild-type and natural-variant gC1q domain (stability and self-association assays) with and without Ca2+

   PMID:34445792

   Open questions at the time

   • Single lab with no independent replication of the biophysical findings
   • Effects measured on the isolated gC1q domain rather than full-length Otolin-1 in its native otoconial matrix
   • No direct demonstration linking these residue variants to otoconia/otolith formation defects or balance phenotypes in vivo

• How OTOL1 oligomers integrate into the otoconial matrix and contribute to balance sensing at the tissue level remains unresolved.
• No identified physical partners within the otoconial matrix
• No structural model of the assembled trimer or higher-order assembly
• No in vivo or animal-model validation of mutational effects