Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme, which is required for motile cilia beating (PubMed:34715025). Important for proper ciliary and flagellar beating. May act in cooperation with CFAP45 and axonemal dynein subunit DNAH11. May play a role in cell growth and/or survival (By similarity). Interacts with BRCA2. Interacts with the CCT chaperonin complex. Interacts with HSP70. Interacts with AK8. Interacts with CFAP45. Interacts with DNAI1 (By similarity). Interacts with IQDC (By similarity). Located in the proximal region of respiratory cilia. Expressed in trachea multiciliated cells. Belongs to the CFAP52 family.