@article { doi:10.1073/pnas.2207605119, title = {SPACA9 is a lumenal protein of human ciliary singlet and doublet microtubules}, journal = {Proceedings of the National Academy of Sciences}, volume = {119}, number = {41}, year = {2022}, pages = {e2207605119}, abstract = {The cilium-centrosome complex contains triplet, doublet, and singlet microtubules. The lumenal\ surfaces of each microtubule within this diverse array are decorated by microtubule inner proteins (MIPs). Here, we used single-particle cryo-electron microscopy methods to build atomic models of two types of human ciliary microtubule: the doublet microtubules of multiciliated respiratory cells and the distal singlet microtubules of monoflagellated human spermatozoa. We discover that SPACA9 is a polyspecific MIP capable of binding both microtubule types. SPACA9 forms intralumenal striations in the B tubule of respiratory doublet microtubules and noncontinuous spirals in sperm singlet microtubules. By acquiring new and reanalyzing previous cryo-electron tomography data, we show that SPACA9-like intralumenal striations are common features of different microtubule types in animal cilia. Our structures provide detailed references to help rationalize ciliopathy-causing mutations and position cryo-EM as a tool for the analysis of samples obtained directly from ciliopathy patients.}, doi = {10.1073/pnas.2207605119}, url = {https://www.pnas.org/doi/abs/10.1073/pnas.2207605119}, author = {Gui, Miao and Jacob T. Croft and Davide Zabeo and Vajradhar Acharya and Justin M. Kollman and Thomas Burgoyne and Johanna L. H{\"o}{\"o}g and Brown, Alan} }