Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme, which is required for motile cilia beating (PubMed:36191189). Suppresses cell death induced by accumulation of unfolded Pael receptor (Pael-R, a substrate of Parkin) (PubMed:14532270). Facilitates the formation of inclusions consisting of Pael-R, molecular chaperones, protein degradation molecules and itself when proteasome is inhibited (PubMed:14532270). May play an important role in the formation of Lewy bodies and protection of dopaminergic neurons against Parkinson disease (PubMed:14532270). {ECO:0000269|PubMed:14532270, ECO:0000269|PubMed:36191189}. This is the function of PACRG (parkin coregulated, ENSG00000112530).