Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme, which is required for motile cilia beating (PubMed:34715025). May play an important role for the maintenance of myelin-axon integrity (By similarity). May affect intracellular Ca(2+) homeostasis (By similarity). Expressed in trachea multiciliated cells.