Otolin (OTOL1), also known as C1qTNF15, is an approximately 65 kDa protein found in the otoconial membrane lining the cochlea and vestibular labyrinth of the inner ear. Collagen-like protein specifically expressed in the inner ear, which provides an organic scaffold for otoconia, a calcium carbonate structure in the saccule and utricle of the ear. It associates into multimers and disulfide-linked oligomers and also associates with other otoconial proteins including and Otoconin-90 (also known as PLA2G2A, PLA2L, and phospholipase A2 homolog) and Cerebellin-1. It is extensively glycosylated and has multiple hydroxylated proline residues in the collagenous regions.