N'-terminal- and Ca2+-induced stabilization of high-order oligomers of full-length Danio rerio and Homo sapiens otolin-1.

Otolin-1 is a C1q family member and a major component of the organic matrix of fish otoliths and human otoconia. To date, the protein molecular properties have not been characterized. In this work, we describe biochemical characterization and comparative studies on saccular-specific otolin-1 derived from Danio rerio and Homo sapiens. Due to the low abundance of proteins in the otoconial matrix, we developed a production and purification method for both recombinant homologues of otolin-1. Danio rerio and Homo sapiens otolin-1 forms higher-order oligomers that can be partially disrupted under reducing conditions. The presence of Ca2+ stabilizes the oligomers and significantly increases the thermal stability of the proteins. Despite the high sequence coverage, the oligomerization of Danio rerio otolin-1 is more affected by the reducing conditions and presence of Ca2+ than the human homologue. The results show differences in molecular behaviour, which may be reflected in Danio rerio and Homo sapiens otolin-1 role in otolith and otoconia formation.