Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme, which is required for motile cilia beating (By similarity). 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 (PubMed:33139725). Interacts with AK8; dimerization with AK8 may create a cavity at the interface of the dimer that can accommodate AMP (PubMed:33139725). Interacts with CFAP52 (PubMed:33139725). Interacts with ENKUR (PubMed:33139725). Directly interacts with DNALI1 (PubMed:33139725). Interacts with DNAH11 (PubMed:33139725). Interacts with DNAI1 (PubMed:33139725). Located in the proximal region of respiratory cilia. Expressed in respiratory cells and in sperm (at protein level) (PubMed:33139725). Expressed in nasopharyngeal epithelium and trachea (PubMed:10524255). The disease is caused by variants affecting the gene represented in this entry. Belongs to the CFAP45 family. Truncated N-terminus.