Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme, which is required for motile cilia beating (PubMed:34715025). It is an AMP-binding protein that may facilitate dynein ATPase-dependent ciliary and flagellar beating via adenine nucleotide homeostasis. May function as a donor of AMP to AK8 and hence promote ADP production (By similarity). Interacts with AK8; dimerization with AK8 may create a cavity at the interface of the dimer that can accommodate AMP. Interacts with CFAP52. Interacts with ENKUR. Directly interacts with DNALI1. Interacts with DNAH11. Interacts with DNAI1. Located in the proximal region of respiratory cilia. Expressed in trachea multiciliated cells. Belongs to the CFAP45 family.