Tight junction-associated protein that is involved in the survival of auditory hair cells and hearing. Maybe by modulating the barrier properties and mechanical stability of tight junctions (PubMed:26609154). Has no peptidase activity (PubMed:26609154). Interacts (via the C-terminal region) with the heterodimer TJP1:TJP2. Expressed in the cochlea. Isoform 1 expression levels are 10-fold higher than isoform 2 expression levels. Belongs to the peptidase C19 family. Although the active site residues are conserved, lacks the conserved His residue which is normally found 9 residues before the catalytic His. Chimeric cDNA.