Natural Mutations Affect Structure and Function of gC1q Domain of Otolin-1

Abstract

Otolin-1 is a scaffold protein of otoliths and otoconia, calcium carbonate biominerals from the inner ear. It contains a gC1q domain responsible for trimerization and binding of Ca2+. Knowledge of a structure–function relationship of gC1q domain of otolin-1 is crucial for understanding the biology of balance sensing. Here, we show how natural variants alter the structure of gC1q otolin-1 and how Ca2+ are able to revert some effects of the mutations. We discovered that natural substitutions: R339S, R342W and R402P negatively affect the stability of apo-gC1q otolin-1, and that Q426R has a stabilizing effect. In the presence of Ca2+, R342W and Q426R were stabilized at higher Ca2+ concentrations than the wild-type form, and R402P was completely insensitive to Ca2+. The mutations affected the self-association of gC1q otolin-1 by inducing detrimental aggregation (R342W) or disabling the trimerization (R402P) of the protein. Our results indicate that the natural variants of gC1q otolin-1 may have a potential to cause pathological changes in otoconia and otoconial membrane, which could affect sensing of balance and increase the probability of occurrence of benign paroxysmal positional vertigo (BPPV).

High Serum Levels of Otolin-1 in Patients With Benign Paroxysmal Positional Vertigo Predict Recurrence

“…The otoconia organic matrix is composed of a variety of proteins, the chief constituents of which are otoconin-90 and otolin-1. Otolin-1 is a secreted glycoprotein whose mRNA expression is restricted to the support cells of the vestibular maculae, semicircular canal cristae, and organ of Corti and marginal cells of the stria vascularis ( 10 , 21 ). Parham et al first reported that otolin-1 could be detected in serum and that the levels were higher in patients with BPPV than in healthy controls ( 11 ).…”

Challenges and Current Research Status of Vertigo/Vestibular Diseases

“…Otoconin-90 Located in the supporting cells of the organ of Corti and the vestibular macula (Lundberg et al, 2015) The main matrix protein of otoliths, promotes otolith nucleation and growth (Lundberg et al, 2015) Elevated serum OC90 levels in patients with benign paroxysmal positional vertigo (Bi et al, 2021); Reduced balance in knockout mice (Zhao et al, 2008) Otolin-1 Located in the supporting cells of the organ of Corti and the vestibular macula (Hołubowicz et al, 2021) Otolith scaffolding protein, is involved in the formation and correct positioning of the otolith and its correct anchoring to the sensory macula (Weigele et al, 2015) Elevated serum Ootolin-1 levels in patients with benign paroxysmal positional vertigo (Wu et al, 2020) Otolith Matrix Protein-…”

Advances in otolith-related protein research

“…Otolin-1, a scaffold protein for otoliths, is found in the extracellular matrix of the inner ear and contains a C1q-like structural domain that forms a stable trimer in the presence of calcium ions and is responsible for Ca 2+ trimerization and binding (Hołubowicz et al, 2017(Hołubowicz et al, , 2021. OC90 can bind to Otolin-1 and build a protein-rich matrix that serves as a scaffold for subsequent calcium carbonate deposition (Thiessen et al, 2019).…”

“…Otoconin-90 Located in the supporting cells of the organ of Corti and the vestibular macula (Lundberg et al, 2015) The main matrix protein of otoliths, promotes otolith nucleation and growth (Lundberg et al, 2015) Elevated serum OC90 levels in patients with benign paroxysmal positional vertigo (Bi et al, 2021); Reduced balance in knockout mice (Zhao et al, 2008) Otolin-1 Located in the supporting cells of the organ of Corti and the vestibular macula (Hołubowicz et al, 2021) Otolith scaffolding protein, is involved in the formation and correct positioning of the otolith and its correct anchoring to the sensory macula (Weigele et al, 2015) Elevated serum Ootolin-1 levels in patients with benign paroxysmal positional vertigo (Wu et al, 2020) Otolith Matrix Protein-1 (OMP-1)…”